I take every one apart. That was instilled in me in tech school in the 80s. You don't have to blueprint - I never do, But you need to clean them out, check things, make sure the relief valve functions, and adding a little grease on the rotors will pull the oil up a lot faster when you preoil.
I agree that blueprinting is overrated since I witnessed a scrap oil pump having zero effect on pressure once before.
It was after the 1st fire up on a 440. With 10w30 it had too much oil pressure. Probably due to tight clearances. Nobody was willing to change the clearances so we removed the brand new pump, easy job on a big block. Installed the high mileage pump that was in the scrap bin from before the rebuild. I was skeptic, not due to clearances but the obvious signs of scoring on the rotor.
Anyways after the pump swap there was ZERO change in pressure. This was according to a large sweep Autometer with 1 psi graduations.
