I built one years ago. No idea of power, but it was easily quicker than a standard cossie. It was just blowing through a carburettor though. Crappy old thing built for buttons.
With modern fuel injection and turbos etc, it would be very easy to build one to make some power.
Cant really see why there would be any big problems. The bottom end is pretty mcuh same as a Cossie for a start, and the head aint that bad.