521 super uses a different head and pipes. If you want it RIGHT,you can't just buy the parts off the "shelf" . To properly setup a super, the domes must be spot on and proper pipe selection is critical. I suggest having a builder that is extremely familiar with supers to do it. A little FYI,,, all Supers are not the same. A builder familiar with them can fill you in on the rest.
Lap the flywheel to the crank snout. The key dosen't do crap except index the flywheel. If you're expecting it to hold the flywheel on , you're in trouble.