These are the .veh files that separate the P1 class in Mikks mod, so only P1 cars race against each other in the same race. Also the realfeel description is changed so it is just one entry for the P1 class rather multiple entries for each car/skin.
This will place the cars in the Camaro section
Extract to your GSC Extreme folder.
Recommended real feel values (thanks Fernando Zart). Just copy and replace the ESGT2MaxForceAtSteeringRack=-2000.000000 entry in the realfeel settings with this.
Oh aye, make a backup of your files first in case you want to revert back