Yes you can have both and it won't interfere with your regular GTR2 install. They should just show up as new classes.
Personal opinion and biased here, but if it were me, I'd wait until the GTL to GTR2 version covered in our thread in the gtr2 mod section is out before adding the other. Most guys have had some issues with the install of the files that are floating out there and they are not ours. The V8's should install without a hitch, though.