I have 700 miles on the rebuild of a 440. Oil pressure has been fine at about 60/65 on the highway. Yesterday was a 100 degree day. Water temp was 3/4 on the gage up from the usual 1/2 way point. I could see the oil pressure drop as the temp went up. It went to 45 at 70mph. Idle was still around 15. I use 20/50 VR1. I think this is a bearing clearance issue and no change to the pressure relief valve setting will really alter things, right?

I assume you were turning the engine well below 4500 RPM, 10 pounds per thousand RPM is considered fine oil pressure.

Your engine was running significantly hotter. So the oil is thinner - and the pressure drops. I'll bet there is nothing wrong with it other than a marginal cooling system. Do you have a temperature gauge that is calibrated?

Best way to verify this is "normal behavior" is to see if the pressure is back where it was on a cooler day...

Could also cut open your oil filter and look for metal.

Right; you have a volume issue, not a pressure issue. Was a standard volume pump installed?