Quote from an Email from a mate in Thailand
Well, the problems are nothing is a great fit for what we have. Firstly the crank.... There is no easy crankshaft conversions available. Honda crank is the closest but finding 56 OD bearings to suit the small 20 ID honda cant be obtained.
Crankpins are another matter however. You can use typical Honda offset crankpins in these, with choice of 94,97,100 or 103mm conrods. The difference is the width of the conrod big end is 16mm with the honda 14mm. A couple of washers seems to be all thats needed and has been done in a fair few 150/160's. The reliabilty issue is rediculous though. They never last because the cranks cant hold out even with weird and wonderful crankconversions that have been made that we hear about.
So it would be best to keep it relatively tame!