The dirt-bike, or early ATV rear axle setup would be good.
Pivot your live axle from a slightly forward cross-shaft, and use two short chains,
one from the engine to the shaft, and one from that shaft to the rear sprocket.
A couple of mini-bike coil-shocks mounted at the rear axle should do well.
Lots of good drive parts here:
http://www.northerntool.com/webapp/w...egoryId=544613