Try looking for an old Yamaha QT50 or also known as the Yamahopper moped, I think these were shaft driven and would be pretty easy to lace the canter hub to a bicycle wheel... Another plus, or could be a problem depending on what's wanted is that these were single sided swing arms so one could mount it as a functioning swing arm and have rear suspension as well. Otherwise, the shaft could be trimmed and made to adapt to just about any small engine and should be able to withstand up to about 10hp or so.