Re: Which engine?
I have some experiencie with industrial (sorry but I donīt know the name of the device... electric generators? The engines used to power factories in case of a blackout), 4-stroke, low size (125 to 500 cc) engines. I think the "metals" (crankshaft, pistons, rings, cylinders) are WAY more resistant than the "china girl" equivalents. The engine is a bit more complex as well, and it is heavier and lower-performing.
However, if only u$200 are to be spent, and this is the first engine heīll buy... I would advise for a good china girl kit. I have the cheapest 48 cc engine with bearings (not bushigs) that I could find, I havenīt had a problem in 4 gas tanks. That should be enough to get some advertisment going with his proyect, I guess! He can always change the motor later on.
Oh, and then thereīs the sound issue. In my humble opinion, in small displacements, 2-stroke engines do sound a bit better!