i took the rear wheels off a couple of thunderjet slot car pull backs and put them on one of my clones all round. they're wider than the bit wheels and the same diameter as the bit front wheels. they look and work great. it looks pretty cool with the wider tires all the way around. i also took the front bit wheels that were left over and put them on the back of another car. this looks more realistic and runs great. i did'nt seem to lose any performance at all that i can tell. it's cool having some different looking cars.
Are you talking about the "Johnny Lighning" Thunderjet models, or the 60's "Model Motoring" ThunderJet 500 slot cars? I have an old Model Motoring slot car setup with a dozen cars from about 1965. I wouldn't dream of parting them out for BCG mods!