For you GP460 engine owners, the OEM clutch retails for $54. Then you have to change the 8000rpm engagement springs, which cost $15.
davesmotors.com sells pocket bike clutch with a tapered shaft and keyway. These fit the 460 engine perfectly, and engages softly, right off idle. My older 460's crankshaft has the keyway, but its original clutch doesn't. Use the $9 pocketbike clutch, grind down the 460 special retaining crank nut/washer and use the 460 flywheel key for the clutch key.