Yes the 55 to 64 oil pump shafts should all be hex so the end of the distributor should be female hex (as should be the oil pump). The only difference should be found with the 54 239's that had the tang drive.
One piece of advice for you on the distributors for Y blocks. The 54-56 Fords came stock with a vacuum advance only that was matched to the particular 54-56 Carb signal. 57's and up are very different in the signal department. Those old 54-56 distributors were called "load-a-matic"... they might as well be called "load-a-crap". There was no centrifugal, mechanical advance in these distributors. If you are replacing your original 56 distributor for a distributor that will now have mechanical advance, please either replace your stock 56 carburetor OR modify your stock 56 carb to give a proper signal to the new distributor OR at least plug the vacuum port on your stock carb and run the vacuum to your manifold at the very least. By the way, Ted Eaton, a moderator on this site has an excellent article on modifying the original 2 barrel and 4 barrel 54-56 Ford carbs so that they will run correctly with the better distributors.
Happy Y blocking!
Daniel JessupLancaster, California
aka "The Hot Rod Reverend" 
check out the 1955 Ford Fairlane build at www.hotrodreverend.com