marksb'ville's memory is right, and mine was wrong. One summer in the late '70s, it seemed like all I did was rebuild unit 650/750 motors-or more accurately, replace crank bearings. Not only did we leave the gearbox internals in place, we also lefft the cam gears on.
If it hasn't been mentioned already, pull and clean the sludge trap. and repalce the rod bolts.
Wherever you are Dad, thank you.