what cylinder heads, as mentioned I have seen oil pool up top and drop oil pressure. My personal engine I had in my old boat was a 548. had V-1 AFR heads, 14 qt oil pan. Had great oil pressure w 20/50. , dynoed it once with 5w/30 or something, had great oil pressure. Attempted to run it in boat with a 5/30 or 5/40, when oil got over 200 degrees, oil pressure would drop as rpms went past 3800/4000. I was running closer to .003 mains and .0028 rods but did have priority main Dart big M block. Did a filter cut, no metal, went back to 20/50, 65/70 psi at 6300 hot.
Fast forward, ran it just playing around on my dyno without the blower for fun trying parts. First issue I had was with a Canton 10 qt pan (14 qt was swapped), when engine got upstairs after 5 or so seconds, oil pressure would start rapidly flickeriing/down 20/30 lbs from 60/70 , added a qt of oil, was slightly better. Pulled breather off at exact second it was doing it (with 2 people), heads were flooded with oil, again, V1 AFRs that had small drain back holes. The 14 qt pan evidently masked that issue previously. tore heads off on dyno, opened up drain back holes similar to the AFR V-2s, pulled pan to inspect bearings, bent the reallly stiff trap door springs a little and when I reran it with normal amount of oil, isuue went away.

Anyone think that the oil bypass valve is opening at the 3800 RPM. Maybe have the 11 psi valve vs the 30?

I wonder if he has a mark 4 block,,his roman numerals says so,unless confused.then he should have follow artic and I on removing those bypass's in gen 5 and 6 blocks.

https://duckduckgo.com/?q=roman+nume...or-9047698.jpg

block is mark 4 and the bypass it had was in the old line adapter that mounts where a filter would in a automotive application. i removed it and put a billet hardin marine oil block adapter on it that does not have a bypass provision any longer. the heads are merlin 1-043 and we did run it up to as high as 3900 rpm and pulled breathers while doing so and there is oil draining back and not pooling up in the heads

humm,,how close is the oil pump pickup to the bottom of the pan?you have that measurement?

the pickup I'm using sits higher in the front than it does in the rear slightly but the closest portion is a little over 1/4"

All that would do is keep all of the oil from being filtered. If anything it would help oil flow.

Correct, flow is inverse proportion to pressure. You eliminate the restriction therefore you loose pressure and increase flow. I believe he said he had a loss of pressure issue not a flow issue. I don't think he has checked flow as of yet.

the only bypass in the system is the bypass in the oil pump.... all others have been removed

You have not mentioned oil temps at all?? Have you checked them??
I also would not be using 10w-30 in any marine engine