I guess the better thing to ask at this point....
What is the motor being used, and what is this being used for... Bike 4 wheeler...
Well I was planing on building the engine... I was thinking about making a small OHV 400cc (or whatever size, more then 6.5hp) v-twin, I would use the pistons and cam and maybe crankshaft from a gx200 and I would make the cylinders, crankcase, heads, and all that good stuff. Also I would have automatic intake valves (cool looking and would make it a bit simpler) I have drawn quite a few pictures and I have a great understanding of how and what I would do. That said I don't have a machine shop and or access to one. In the spring I want to make a shed and get a mill, lathe, pipe bender, tig welder (or make an hho welder) and just the basic machine shop tools. As of now I can't actually make the engine so it's just ideas for down the road.
In the meantime I think I could rig it up to 212 and slap it on a mini bike (for testing purposes...)
Also my plan for the future is I would make a 3-speed-v-twin-hard-tail-flat-tracker-maybe-street-legal-vintage-looking-little-motorbike...