Thanks very much, the pair of you.
There wasn't a readme, but the information I needed I skipped past on the website I downloaded it from, and it was the GTL-GTR2 mod (made obsolete by Power & Glory I understand) that I needed. I thought it was simply information detailing that it had been converted from GTL and that it was a standalone car. Ah well, at least I know now for future reference.
The car-sharing between mods was a big reason I finally made the switch from RFactor to GTR2, even though I've had the retail disc for the latter a lot longer than I'd care to admit. Other than open-wheel racing (which F1C does better anyway due to the car/driver differences), I really don't see how the former became the most well-known of all the GMotor-based racing sims, when GTR2 was basically the same game but with an extra year of development, so you had stuff like weather changes and driver animations that the other lacked. Ah well.