Before you go to the trouble of replacing the oil pump, try switching to a straight 30 weight oil, not a multi-viscosity like 10W-30, etc. If the pressure rises noticeably, the pump isn't the problem, bearing clearance is. It might be possible to remove shims from the main bearing caps and close up the oil clearance slightly, but be sure to check for proper clearance with Plastigauge or by using a small piece of shim stock between the main bearing and the crankshaft to see what the clearance is. For instance, if installing a small piece of .002" shim between the bearing and the crankshaft results in very stiff rotation, That's the oil clearance. I like to fit the bearings to about .0015" to .002" clearance if possible. The rod bearings can be checked the same way, but they won't affect oil pressure because of the dipper system- - -there's no direct oil pressure supplied to the rods. Check the oil distributor valve to be sure it's keeping most of the oil flow to the bottom end of the engine. The oil supplied to the cylinder head has reduced pressure to direct most of the flow to the main and cam bearings.
Jerry



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