You'll also need the early oil pan and pickup, dipstick and tube.
You'll need to run the early carb too, since the throttle linkages are different ('62 has a mechanical bellcrank type throttle, '81 has a cable throttle).
I figured I would use those parts from the take out engine. W some linkage mods to run a larger carb and retain the trans kickdown.
My concern is the transmission mating.
The newer engine has a larger ID in the end of the crank and the early 904 has a smaller OD on the nose of the converter. I figure the outer mounting holes on the flexplate should not be relied to maintain concentricity to the converter. Looking for longevity.
Also heard I may need a later flex plate.