I’m working on a 75 and I think they are the same.
I have mine cleaned up but I’m waiting on the
crankshaft seals before I separate it. "BUT" after you
disconnect the neutral clutch cable it would seem
you just take the screws out around the bottom to
remove the powerhead. The drive shaft is splined
with a tube that surrounds it. The tube seated with
an O ring that may separate there or come out with
the powerhead depending on where it is stuck the
most. There is just an O ring on the other end as
well and it is seated in the water pump. You can see
the tube in the clutch cable picture.
A "Boathouse Repair" is one thats done without having tools or the skills to do it properly.