From an old post at Nogrip:
"GTL-GTR2 conversions are very easy.
1- Rename each .gtl file to .gtr
2- Open .cas file with text editor and rename the lines MasFile=xxx.GTL in xxx.GTR
except stex.GTL and talent.GTL because you need the GTL ones. You can do two things:
if you have GTL, copy and paste them in your Teams folder
else you can use the stex_GTL.gtr and talent_GTL.gtr in the mod by SCCA1981
(and paste their name in the .cas file)
3- Open .car files and change the filter in the line
Classes="------" to match your category
Done.
/////////////////
it's easier than that,
you need stex.gtl and talent.gtl copy them to gtr2 install what gtl mods you want,
if the skins don't apear you need to change .gtl to .gtr "
In a few cases you will get CTDs, this is usually when a mod calls wheels or other items from another mod or from a separate download. Check the trace file.