NFSUnlimited.net

learn hex editing and how to edit the vinyls. it isn't easy, i've been messin with the prostreet files for a long time and stuff don't understand a lot of it

reinstall your game, and redownload the 1.1 patch from a different place. Some of the 1.1 pc patches i discovered DONT come with those cars files for some reason

it probably is possible through hex editing but it would take a long time and experience with editing