I think Jim pretty much covered it.

You can take a ball shape burr and relieve the inside edge of the sharp 90 degree turn that the suction side oil passage makes in the block.

Also, the last 3 Melling pumps that I worked on were badly misaligned between the pump body and cover, as observed where the oil passages are to line up (at the o-ring). They were bad enough that I had to open up the cover bolt holes, rotate the cover slightly and then drill and roll-pin the cover to the body.