You can do it... but usually its easier and more reliable to just bolt in a
Rotax. Jap bike engines usually present the problem of having to deal with the
unitized tranny. And there is always the concern of overheating. There are a
few Harley / S&S / equiv. powered machines out there too. Just depends on the
trade-offs you want to make. USU's carbon-fiber Wright Flyer is using what
looks like a Harley EVO motor.

Harry