Alan: I think this is an idea worth trying if one had the extra cash to invest. However a car engine has that big heatsink on it because there isn't much air flowing across it. The problems that you might run into is that you need a motor with an rpm range that will work with the 'chopper. If not you will be forced to try to mach the head speed by changing gears in it. As I mentioned about the head of the car engine, a chopper has much more air flow to the head which will make the engine run cold and might not have the same amount of power in the air as it does in a car.
Dan