I don't know what the proper clearance dimensions are but would guess that they would be that same as those in the service manual.

I think that there is something in the tech archives on oil pumps mods, or tuning.

What I found on the last three new Melling pumps (standard rotor) is a very poor alingment between the body and head pressurized oil passage at the o-ring. They were bad enough that I enlarged the mounting holes and drilled for roll pins after fixing the alignment problem. I then ream the oil passage in the pump body to better match the hole size in the pump head. I don't know if anyone has seen this in the HV units.