Most of the guys around here that build those carts use a high hp snowmobile set up. driving/ driven centrifugal clutch’s, Jack shaft, chain case. No shifting, gears up steadily until driver is open and driven is closed. With the right weights, rollers and springs it’s a amazing setup. Had the old SRX 700 yamy over 100mph many times. Comet is a good Brand name in those clutches