Kevin, there is this thing, called an Internet. Did anybody ever tell you how it's architecture is set up? Give it up, you lost.
Ahem . . . On to breaking the Fanwork Ban! (The Defend IP Act must have a clueless fan boy with irrational man love for it somewhere in Michigan -- or wherever he lives now.)
RIFTS is something of a game where you take Tolkien's Middle Earth, World Mythology (I don't know why you would, the First Story is based on a Planetary Constellation anyhow), the tropes of Science Fiction, 4 color Superhero comics, the Old West, Anime, and Horror of all kinds. Put it all in a pot, add water, simmer and stew. What you get is the Chop Suey of all RPG settings. However, I say Chop Suey instead of Goulash because it actually tastes good and goes down easy.
The system is worthy of converting to d20, because d20 still has a lot going for it that makes the Palladium System look like it's 30 years old (actually, 40, but whose counting?)
The major problems are these:
Mega-Damage: Most fans say -- use SDC damage, it's much better. Convert everything over to SDC and use SDC weapons. However, I say use a rule in d20 that would work that much better. It's called Damage Reduction.
Some magic creatures have the supernatural ability to instantly heal damage from weapons or ignore blows altogether as though they were invulnerable.
The numerical part of a creature's damage reduction (or DR) is the amount of damage the creature ignores from normal attacks. Usually, a certain type of weapon can overcome this reduction (see Overcoming DR). This information is separated from the damage reduction number by a slash. For example, DR 5/magic means that a creature takes 5 less points of damage from all weapons that are not magic. If a dash follows the slash, then the damage reduction is effective against any attack that does not ignore damage reduction.
Whenever damage reduction completely negates the damage from an attack, it also negates most special effects that accompany the attack, such as injury poison, a monk's stunning, and injury-based disease. Damage reduction does not negate touch attacks, energy damage dealt along with an attack, or energy drains. Nor does it affect poisons or diseases delivered by inhalation, ingestion, or contact.
Attacks that deal no damage because of the target's damage reduction do not disrupt spells.
Spells, spell-like abilities, and energy attacks (even nonmagical fire) ignore damage reduction.
Sometimes damage reduction represents instant healing. Sometimes it represents the creature's tough hide or body. In either case, other characters can see that conventional attacks won't work.
If a creature has damage reduction from more than one source, the two forms of damage reduction do not stack. Instead, the creature gets the benefit of the best damage reduction in a given situation.
Damage reduction may be overcome by special materials, magic weapons (any weapon with a +1 or higher enhancement bonus, not counting the enhancement from masterwork quality), certain types of weapons (such as slashing or bludgeoning), and weapons imbued with an alignment.
Ammunition fired from a projectile weapon with an enhancement bonus of +1 or higher istreated as a magic weapon for the purpose of overcoming damage reduction. Similarly, ammunition fired from a projectile weapon with an alignment gains the alignment of that projectile weapon (in addition to any alignment it may already have).
Weapons with an enhancement bonus of +3 or greater can ignore some types of damage reduction, regardless of their actual material or alignment. The following table shows what type of enhancement bonus is needed to overcome some common types of damage reduction.
There you have it, Damage Reduction. Damage Reduction can effectively replace Mega-Damage points. For biological creatures made with carbon-based chemistry. Vehicles and piloted Robots (Mecha) have something similar -- Hardness.
Skill System based on a percentile: Okay, there is a lot of skills. Only SpaceMaster and Rolemaster beats the number of Skills. However, they are based on percentiles and you have to roll low to succeed in your skill. However ICE was experimenting with Target Numbers with their Middle Earth Adventures RPG, and this became the basis of Shadowrun and other modern RPGs. Roll a die, beat the target number, and you succeed.
The d20 System uses a TN-based skill system, called DC.
P.P.E., ISP casting system: The spells can be cast by any wizard by any level. The psychics can cast psychic effects based on their effective power level. This is governed by Potential Psychic Energy and Inner Strength Points. This is basically to replicate book wizards. But Authors have one superiority over games. Rifts is a goal-oriented game (i.e. uses Levels). An Author can write a story about a befuddling wizard's Apprentice who can control the weather.
Pathfinder still uses the casting system based on Jack Vance's Dying Earth series, but there are ways to overcome this (Advanced d20 Magic anyone?).
Combat Progression: As you attain more levels, your combat experience increases. This isn't half bad, as the Palladium game system is rules oriented. And yes, you do get better at hitting and/or killing people as your experience increases in real life.
While combat systems in Rifts are leveled, however, the Pathfinder/d20 System uses feats -- leveled feats -- to achieve this. Fortunately, you can get feats every odd level or so.
O.C.C.s: Last point, the Occupational Character Class is blown up out of proportion in RIFTS. Great idea, poor execution. Similarly, the prestige class has been also blown out of proportion during Wizards' run of the d20 System. In Pathfinder, you don't have this problem, but you're getting into the problem of Class Bloat.
So, basically, you have to limit your class options.
For a Rifts conversion to Pathfinder you will need:
* One Rifts book, you might have several.
* Pathfinder RPG (Paizo)
* Pathfinder's Bestiary and Bestiary 2
* D20 Modern (WotC)
* D20 Modern Weapons Locker (WotC)
* D20 Mecha (Guardians of Order, defunct -- or Dream Pod Nine)
* Dragonstar Players Handbook or D20 Future (for laser and other energy weapons)
to go around the "Theme Park" of Rifts you might find these handy:
Rifts: England -- Pick up a copy of the Arthurian Legend for Pathfinder. I think it's made by RPG Objects. Sprinkle in a copy of (3e) Forgotten Realms -- especially the Dalelands and Cormyr; and simmer. Don't forget the laser weapons!!
Rifts: New West -- Deadlands d20 with D&D monsters, robot horses with carbines sticking out of their noses, and laser guns! :)
Rifts: Japan -- Pick up a copy of BESM d20 and you pretty much crossed the line into Rifts: Japan.
RIFTS: Dinosaur Swamp -- pick up a copy of Prehistoria d20 from RPGnow.
Superheroes: There are strong differences between Mutants and Masterminds and Pathfinder judging by DC Adventures. While you can have Superheroes in RIFTS (ala Heroes Unlimited), Mutants and Masterminds is the d20 System totally rebuilt around the 4 color Superhero Comic genre. Although you can solve some problems with RIFTS using Mutants and Masterminds 3rd edition, your best bet is to convert the entire game of Rifts to Mutants and Masterminds. And given Kevin Seimbedia's mindset while he wrote Rifts, you might be much more successful at doing so than by using Pathfinder as your base.
Yeah it's weird, but if you read Rifts, the whole thing is ridiculous when trying to apply Real World physics. And Mega-Damage makes sense, how? that kind of stuff. Judging how ridiculous the whole game is, Rifts is probably inspired by 4 color comics.
Since even Marvel and DC have "theme park" locations in their universes, they carry on certain antiquated ideas. And even their heroes are ridiculously overpowered (Superman, for instance, is PL 14, while Wonder Woman is PL 15, while Captain Atom might be misjudged by Green Ronin; while the Hulk maybe the most powerful being in either universe in terms of raw, muscular strength!).
Rifts is, quite simply, trying to stick a 4 color-universe made up of square pegs and putting it into circular holes and using a hammer to force them in. The game works, kinda, but you have to suspend your Disbelief when you are exposed to better games.
Everything Else: You're pretty much on your own.
Since Kevin is ridiculously backward in his thoughts about the OGL, you will never ever see an official conversion of Rifts to d20, or Mutants and Masterminds. There is a clause in the OGL that simply says that Wizards has the right to take your work (but everyone else has the same right). However, due to the amount of material that Palladium has published over the years, I can only focus on the classes in the main book. For the rest, you are on your own.
Borgs: There are no rules dealing with Cyborgs in Pathfinder or in Dragon*Star. In d20 Future, however, there are rules dealing with bionic enhancement (they were published in Dungeon once, I believe).
Coalition Stuff: d20 Modern Fast Heroes and Strong Heroes with the Soldier Advanced Class. SAMAS pilots, however, are Mecha Pilots.
Crazy -- You have Mind over Matter implants that supercharges your brain. I suggest either Smart Heroes or Charismatic Heroes with the MoM implant. Crazies also get a Sanity score and are governed by the Insanity rules found in Call of Chthulu d20.
Cyberknight: Psychic Warrior or Soulknife class with the code of Chivalry. They have cyberarmor bonded to their skin.
Glitter-Boy: Mecha Pilot class from BESM d20 piloting a Glitterboy! :D
Headhunter: Strong Hero, Tough Hero, or Fast Hero with cybernetics. Your typical Shadowrunner.
Juicers: the class that fits the Juicer best is the Fast hero. But remember, they are augmented by chemicals rather than expensive Cyberwear.
--- Body Fixer: Dedicated Hero or Smart Hero with medic advanced class.
--- City Rat: Punked hero -- can be replicated with any d20 modern class except Smart.
--- Cyber-Doc: Dedicated hero with medic advanced class specializing in using Cybernetics to treat injury and disease.
--- Operator: Dedicated or Smart hero specializing in mechanics. Might have some psychic powers, in that case, give the player a wild talent feat and pick 3 psionic powers that can be machine related.
--- Rogue Scientist and Scholar: Smart Hero yet again! One specializes in the Sciences and the other the Humanities. Both may overlap.
--- Wilderness Scout: Tough hero all the way with an advanced class based on survival.
--- Vagabond: Catch all concept, may be any d20 modern class.
--- Ley Line Walker: WIZARD class. Not witch, not alchemist, not sorcerer, and not magus! Wizard. Bar none.
--- Mystic: a PC who plays a cleric that has dipped into the Psion class and sorcerer class for a couple of levels.
--- Shifter: Summoner Class from Advanced Player's Guide.
--- Techno-Wizard: Alchemist or Wizard with item-creation feats. However, we all know that the Artificer from Eberron is a better fit. :)
Dragon Hatchlings: Entirely possible to play.
Psychics -- Psychics are given better treatment with the Rifts: Mindscapes supplement. Again, remember, I'm focusing on the main book so. . .
--- Burster: Psion with Control Flames power who has dipped into the Pyrokineticist prestige class.
--- Psi-Stalker: Psychic vampires who feed off of emotional energy. Psions for sure, but they have unique powers that need to be converted over. Telepath is suggested.
--- Dog Pack: There is a whole RPG supplement called Fursona that deals with this and is for Pathfinder.
--- Mind Melter: The PSION melts my mind! see PSIONICS UNLEASHED!