I did one of those a few years back-
But my engine had been left outside and needed a crankshaft.... an item no longer available... at least not that I could find. My pitted and rusted unit was salvaged by my friendly machine shop, and with a new rod, bearings, and seals I was able to get it back together.
I think I put almost a half a tank of gas through it before I sold it to pursue other projects. Lately I seem to like working on them as much or more than riding them.