Chevy did make attempts to limit oil to the head. I'm more familar with the 58 and up blocks that had either a .062 restriction somewhere in the oil galley leading to the head or the restriction was the design of the rocker arms. . Or the so called special center head bolt with a .062 restriction to limit oil when using a 59 or later block with an earlier head..But I don't know how much of an oil pressure loss occurs if done wrong.
For little money and an hours work,loosen the rocker shaft,remove the center oiling piece,figure a way to plug the oil feed hole.See if it makes any difference.
Low oil pressure after an overhaul might be a missing oil galley plug,it can happen.Or excessive bearing clearance.
Obviously use another gauge to be sure of the oil pressure.
