[Qwertious]

>combustion engines modified

Wouldn't that undercut the point of owning a classic car? If old engines were run on a specific fuel and operate differently when burning ethanol, then you can't get the same experience while running on ethanol.

I'm sure there would be differing opinions on this (and some people might just want the chassis and not even care about the engine), but I'd expect some people to see modifying the engine as heresy. Those people would probably want some sort of synthetic petrol fuel.