I just bought a new crank from handybikes and the 12x15x15 roller bearing for a puch slides right in.
Ed can sell you a garelli HC head that fits pretty well or i think 77 has them now. I've had pretty good luck with mine but there were some issues getting it to fit just right. I haven't heard of anyone else having these problems but me though.
Andy, what kind of problems did that head give you? I had a very mysterious soft seize last summer and could never figure out why. Engine temp was running high despite proper tuning. Any thoughts?