...Oh, by the way - I bought a GY6 the other day... the bonus is they are 12v stators, so you could hook up a car stereo - or perhaps a small air compressor via cigarett lighter inlet if you could wire one in.. downside - four stroke, bogs around 35km/p/h common problem... other upside - dead easy to turn into a trike with an old quad based on similar clone engine... then you can run one on the legal tags too as the frame stamp just screws off...
Back on topic - yeah I have wondered if you can bolt them into your rear dropouts like a diy longtail... I also have a dead suzuki TS50 and am trying to figure work arounds on that - nice wheels, fit into a 24" frame, but then maybe the swingarm off the TS could also bolt in, then run jackshaft... floating off topic again...
The bigger question is whynot just strip the GY6 naked, and then bolt on the top part of a cruiser frame you like, to make it look like a motorised bicycle....
Just quietly though I've read the quad/atv gy6's put out to chain transmission.... now thats handy for MBrs eh?