3dsimed, at first, as you'll need to edit materials.
Once you have downloaded 3dsimed, import the gmt files as objects. Once you have imported the files, rename the wildcard textures. The "wc_team_body1" and similar variations (I think it is that way) is "wccarbody". Body2 and similars (which have the same name convention) are wcextrax (x being 0 to whatever you want) and the windows, which are only "wcwindow". Once you do that, replace the light names with "hlglo_ds", "hlglo_ps", blglo_ds and blglo_ps. Once you're done, export the files to rfactor. When you're done with the 3d and textures, use a MAS tool. After that, it's only replacing file types: Hdc is HDV Aud is SFX The engine files will need to add _engine.ini. same with grb files, where you'll need to add _ratios.ini Tyr is tbc DMG is _damage.ini And you'll need to add a cockpit info. Unfortunately, I don't know how to convert a motec from GTR2 to rfactor and make it work. It's one of my pending subjects when converting cars. I hope I have helped.