"One for the books" SB oil pump fit

ok, i get it now
i take it this was without the distributor drive in place, so it couldnt be hanging up on that?
simple case of the tollerances stacking up against you
the hole in the cap is on the small end, the outside diameter of the nub/boss/spiggot/neck is on the large end

or just a bur somewhere?

but, nothing i ever seen in either one of the two oil pumps i ever handled (put that in there, so rusty knows what category i fall into)