While rebuilding the motor in #388 several years ago, I found the oil pump was the single most difficult component to replace. After locating several “better” cores, I decided to hunt down a NOS or repo, I wanted a “good” pump... this was no easy effort!
Long story short... NOS was unobtainable, and the only repos I could find were poorly machined and so not an option. I ended up brazing up my original housing, remachining the gear bores, and bushing the shaft bores to fit a new SI gear set.
I hope all your pump needs is new gears... but give the pump housing a real close look