I still think they're worth trying... I'v found a couple of Japanese Mini truck importers here in the US and they sell the 12" wheels for the Jap mini trucks and I know they top at around 70mph and weigh around 1400lbs plus can handle a 1000lbs load....
EDit: Added mini truck pic with 12" golf cart wheels.
You cant be serious?!? its dangerous.. fair enough you kill yourself but to risk others lives just because you wanted a "look" is rediculous.
Think about it.
Just because a motor can stand on them and even drive a few times, think what WILL happen when it DOES go wrong as it WILL.
Struth mate, Forget it.. Its a bad idea.
As for show use they sound fantastic, A quick swap around would be easy enough and have the car looking the danglies without killing someone elses kids