Looks like the midsection change occured in 1964. So most any 3hp from 1964-1967 should work. Powerhead removal/installation is “tricky” on the folders because the upper driveshaft has a locating pin like the 5.5/6hp models. The powerhead can not be removed unless the driveshaft pin is properly aligned with the slot in the adapter plate.
….Just did a little investigation on this…Looks like the older crankcases do supercede to the newer style crankcases, so it is possible that the older powerheads will fit. But, beware of superceding “backwards”, then can bite you in the butt….So, I will stick with the recommendation of using the powerheads from 64-67.
