[tubman]

It looks to me like the relief spring is a little too stiff. Your bearing clearances and oil pump are good enough to produce over 60 lbs pressure at cruise speed with either viscosity, so the relief valve opens at 60 psi, giving the same pressure at speed. The slightly lower pressure at idle is probably a result of the lesser viscosity of the 30 weight oil. Back in the day, people used to stretch or shim the spring to raise the maximum oil pressure. I'm an "8BA guy", but I think accessing that spring is not difficult on the earlier engines, so you may want to take the intake off and see if it is shimmed or maybe even replace it. That being said, 60 lbs is not high enough to worry about. When I had the engine in my Corvette rebuilt, they put in a hi volume/hi pressure pump, and that engine pegged the 60 lb gauge at hot idle. Now, that is excessive pressure!

I would be happy with the oil pressure you are showing.