Hi there, right the easy way to attach that carburator is just get the carb diameter, then the cranckase diameter (where carb goes) and just ask an engienner to make a sleeve on the lathe, I paid just $15 for the big flange he done to fit the walbro in to it, I guess a small sleeve will be cheaper, and at the end it will be as the original one, you want to keep it simple and with less weak points, then what im learning about conversions you need a needle bearing on the conrod, and a hard pin on the crankshaft, I think they must use something like piston pins to machine and press in to the existing one.
Anyway I found this guy here in few forums, Ken Lambert who is doing these conversions, Im just waiting to see how much will be to mine, if is not too bad I might do it before sending my conversion to the sky.

keep in touch!