I see what you are getting at, and it seems quite feasible. Another way would be to have the rotor magnets on a small diameter rotor instead of on a big flywheel. The only reason they are made on a big flywheel is so that the mag can double as a cooling fan for the engine in their original intended applications. I have had motocross motorcycles that have a small diameter rotor instead of a large mag flywheel, and they allow the engine to rev quicker due to the lower rotating weight, and due to the weight being close to the crank centerline.

Some of the Fuji and Zenoah airplane engines are made this way; I wonder if the pieces could be adapted to our conversion engines?

AV8TOR