It is difficult to install reed valves unless the engine is designed for them. On the high performance motorcycle engines, the reed box is angled to feed under the piston and use crankcase windage to boost the reed flow. Some engines also have ports feeding the transfers directly from the reed box. I would like to see a 50cc model engine designed like one of the 125cc Moto-Cross engines. It would produce about 15 HP. That should fly a brick.