Polini 177cc full circle crank

Hi

I´ve got a Vespa sprint with polini 177 cc cylinder, malossi reed intake with a 28mm carb and a Sip road exhaust. It runs good but I want even more power.

I´m looking for the best full circle long stroke crank shaft to fit my engine. It´s a jungle out there, plese help.

And whats the differences between the three malossi heads?!