The file structure is pretty similar, they just named it different, and instead of being in the \gamedata folder they are in their own \rfm folder.
\GameData\Teams in GTR2 is changed to
\GameData\Vehicles in rf1
GTR2 *.gdb file = RF1 *.rfm file. gives the details of the specific mod (in \rfm folder instead of \gamedata)
GTR2 *.car file = RF1 *.veh file gives the info for a specific car within a mod.
GTR2 *.hdc = RF1 *.hdv All the info for the specific car.
GTR2 *.cas = RF1 *.gen graphics settings. RF2 also has a "Spinner.gen" which is usually a simplfied version that doesn't include interiors, stuff you don't see from the car select screen.
GTR2 *.gtr = RF1 *.mas a compressed file with graphics in it.
GTR2 *.aud = RF1 *.sfx The audio file.
GTR2 *.tyr = RF1 *.tbc The tire file.
GTR2 *.sp = RF1 *.pm The suspension file
GTR2 uses specific file extensions for the engine, gear box, damage, headphysics, and probably a few others, rf1 has all of those as ini files.
Only suggestion I would make is to use an override in the rfm file for the sounds, move the sound files into the mod folder and use an override to tell the game to look there. The default game uses \gamedata\sounds, I always move that to gamedata\vehicles\(modname)\sounds, using this in the rfm:
ConfigOverrides
{
VehicleSound=GAMEDATA\VEHICLES\(modname)\SOUNDS\
You might need to copy some default sounds from the main sounds folder to the mod folder, but doing it that way makes it much cleaner to install and remove. You copy the mod folder to GAMEDATA\VEHICLES\ and the rfm file to \rfm and you are done.
