in general any crank that closes after about 65degrees after top dead center you have some blowback from fresh mixture when you drive with a Si carb. the original Piaggio crank closes the inlet after +/- 55degrees after TDC, this is on the save side. The blowback results in less performance in the lower revs. and difficult carb. tuning.
A Mazzucchelli original crank 55 Degr. ATDC
A MazzUcchelli racing crank about 70degrees ATDC
A Pinasco Racing crank 62 degrees ATDC
A Polini Racing crank 70 degrees ATDC
Tameni racing the same as the original crank 55 degrees ATDC
I tried some different cranks on the Polini 210 and the Piansco 57 racing crank gives beter results in the higher revs, the Tameni 57 gives more Torque in the lower revs but can not rev as much as the Pianasco crank. For me more Torque in the lower revs is the way to go. Some like a more reving engine.
When driven with a PHBH carb with a longer inlet track the situation changes.