I think the main issue is having the internal bits of the box coupling centered in the travel available there. You don't want that box coupling to come apart at any time. It's bottle cap crimped top is a pain in the arse. So,,, My plan would be to get the top end of the column correct with snap ring, etc.., then get the bottom portion of the shaft set to box couplings bottom. Unibody flex should push it away from the bottom eventually. Suggesting a little too low would be better than too high.
