I have a 66cc. Yes I did have to drill the holes outward a bit to fit the 8mm studs, I know if you had the engine with the 6mm studs it would probably fit without any modifications. The puch head that I am using is a 1978 50cc, that I scored off of ebay for $10 about ayear and a half ago. Yes lots of compression and yes cooling like I wouldnt believe, and a wonderfull engine sound. The head eliminates a LOT LOT of engine sound and gives it somewhat of growling sound..