OP said "using a classic car chassis". I'm not particularly knowledgeable, but you can make a lot of modifications to an existing car, but building your own fro

OP said "using a classic car chassis". I'm not particularly knowledgeable, but you can make a lot of modifications to an existing car, but building your own from the ground up would be mostly illegal. I think in some sense, the actual "car" is legally only the VIN plate or something like that. My state stop even doing safety inspections recently, and before that they were already pretty minimal; it was mostly a check that your lights and horn worked and that you had at least one mirror.