Clutch choices

I am building a late teens early 20s motorcycle clone from a modified mountain bike `with a 3 hp Briggs and Stratton engine. I `want the thing to go as fast as possible but still be able to go up hills. Any recommendations on clutches and gearing are appreciated. I am currently thing of using a centripetal clutch but was wondering if the variable speed type used on snow mobiles might be better suited?

Thanks!

Mike