I've used Comet converters on mini bikes and my diesel powered GS850. They are okay, but rob a good amount of horsepower due to friction losses. A two speed centrifugal clutch would be nice, but you would have to gear down say, 50% before the clutch to reduce rpm, double the torque and reduce the 2 speeds chain velocity. Without an oil bath for the chains, they would wear out fast at engine crankshaft speed.

Cris