In the late 60's there was a company the sold little plastic cars that were and exact fix onto an Aurora Vintage slot car. Screw holes and all. It might have been an Aurora company. They were 69 cents or something. We bought a lot of them to rebody my beat up slot cars.
I do remember the cigar box bodies... Johnny Lightning did the same 20 years ago... You could probably still find those on eBay...
Next up is a resin 55 Chevy body ..after a bath in Westley's Bleech White and a good wash I will primer it and paint it two tone Blue and white.