Anything is possible with enough time and money, however by the time all is said and done your better off buying a motorcycle engine with a built in tranny and plate clutch. If you did want to attach a tranny, best bet is buying a harley tranny, which is seperate from the engine unlike most motorcycles, but they are very expensive.
As far as faster, if you have a 5 or 6 spd you will be able to achieve a higher top speed than a centrifugal clutch, with better starting torque, all depending on gearing of course.