You could do an engine swap but you can only use an engine that has a 5/8 PTO shaft coming out of the crankcase. The bigger Honda's and Chonda's have all got 3/4 inch (19mm) PTO shafts which is too big to suit the counter weighted sprocket.
Cheers, BB.
I live a 24 Hour lifestyle, but every now and again I seem to fall asleep, well at least that's what my wife tells me.