There are 2 different size oil pumps. pre 1960 it was a small pump and post 1960 a larger pump.
Both sizes of gasket are provided in the kit. Choose the correct size of gasket and make sure the surface of the pump and third part are clean. Use some assembly grease on the gears.
Installing the oil pressure relief and bypass valves.
Take the copper washer / "O" ring from you gasket set. Make sure the seam which is on the face of the washer is facing away from the case and towards the head of the threaded nut..
Clean out the case passageways with WD 40.
Clean the parts with WD 40 and then put a little engine oil onto the spring and plunger. Put into position and tighten up with a large screwdriver.
Give it a final tighten with a vice grip. Use an old cloth to stop the jaws damaging the head of the bolt.