This is exactly what I have been trying to figure out. I saw a picture of an integra which had what looked like Nascar wheels fitted to the rear, but they were actually flush inside the arches like a drag racer.
I have tried buying an RM 69 Camaro and then adding the body of the normal premium Camaro. The body seemed to reset the cars chassis back to standard, althought the thumnail still shows the RM...