I'm not sure that Chinese trashed engines are any cheaper than the Japanese they copy, nor are any able to just unbolt the trans and add an input sprocket. Substantial cutting, machining, and welding were required on the few I've seen done. The 2-stroke single would have a clutch, oil-tight trans with integral clutch, and would only require adapting a sprocket to replace the stator, removing the rod and pressing crank back together, adding a couple welds. Slip a sprocket on the ditch pump, and away ya go.
http://rover.ebay.com/rover/1/711-5...0001&campid=5335845805&icep_item=283310288518
http://rover.ebay.com/rover/1/711-5...0001&campid=5335845805&icep_item=283310288518