If you have the sliding gear transmission now, a later model transmission you will have to use a later clutch housing. The bolt pattern on the sliding gear 4 speed and the SM420 and SM465 is different. A later clutch housing will bolt to your engine, but there is something else that needs to be modified. Possibly the starter or clutch linkage. If there is nothing wrong with the sliding gear transmission, I'm not sure its worth replacing it with a later transmission. I agree that learning what to drive what you have is not a bad idea.
