This is my friends web store. http://umotobikes.com/
I do almost all of my 2 stroke builds with his 66cc and I think they are one of the best. I am going to be building the performance 2 stroke motors for the site, he works hard with the factory and tries to offer very good kits.
He has 2 good examples of the Huasheng 4 stroke kits. I am with you on the kit build but if the bike has room the HF79cc is probably a pretty bomb proof motor. I think one short cut might be the build kit minus motor on gasbike.net and one of their 4 stroke bolt on mounts. That leaves the transmission. Affordable go karts web store might have the answer, or pedal it up to about 30 and run a straight centrifugal clutch?