the problem with the air cooled scooter kits is that they are all forced-air cooled, the scooters have cooling fans. The heat transfer rate is proportional to the velocity of air moving past the cooling surface so in order to run an air cooled scooter kit on a puch engine, or similar moped engine, you would have to add a fan, modify the cooling fins (weld extra material on?!?) or run it for short periods at a time. The difference in h, the coefficient of convective heat transfer, is on the order of 10-20 times that of a non-forced-air engine for a forced-air engine.
this is why minarellis and scooters can run cast iron cylinders without overheating, and puchs an' shit cant.