Does anyone know if these cars have been modded into GTL? Obviously they are in P&G in GTR2.
No need to mod. There are some very basic steps to convert GTR2 to GTL.
Open the mod (WINZIP or other unzip). Copy it into GTL (most mods will have a Gamedata file) copy that into GTL, say yes when it ask to override the current Gamedata file.
Once in, open a car file, change any GTR file to GTL (right clic, select rename and change the file type to GTL).
Next, Open the car file with note pad and under the "class" line create the new class (you can assign them to SIM_GTC65 or create a new Porsche only class like SIM_IROC)
Next open the CAS file and change all of the misfiles to GTL file type (MASFile=XXX_XXXMASK.gtr to MASFile=XXX_xxxMASK.gtl) except the Talent.gtr and Stex.gtr(I found it's better if you use the original talent.gtr and stex.gtr files (Copy them and place them in the Teams folder.
Next, change any .GTR files to GTL files in the general folder.
If you added the class SIM_GTC65 to the individual car files you should be able to see them in game. If you want to run them separately you can create a new class by opening the SIM_GTC file. Open the Gamedata file and you will see several SIM_G** files. SIM_GTC contains the class file structure. Open this file and where it says Category, add your new class. So add SIM_IROC = IROC. Save the file. This will now add the class to the car selection menu. Add the SIM_IROC to each cars class line to make them appear in the game.
Let me know how it works out.