When I get frustrated over things like this, I often find that I can get a bit of tunnel vision.
I can convince myself that I know exactly where problem lies and proceed to overlook all other possibilities.
I have learned to go for a walk, sometimes a very long one, until I can wrap my head around things better.
I would hate to see you pull the motor apart, yet again, only to find nothing conclusive.

I am with Tim on this one :
"I would also remove and take a close look at the oil filter housing. There is a high pressure bypass valve with a spring inside there. I would inspect to make sure it's assembled correctly."
If that all checks out okay then I would be dropping the pan, pulling the pump and checking the relief valve in the pump.

The only definitive test I can think of short of disassembly, would be to check actual oil pressure where the sender screws in, at least then you might be able to ascertain where the problem is or isn't.
I would think that if you have good pressure at the sender fitting, then the problem would be above that point and would effectively eliminate either the pump or the by-pass.

From what I can discern, the previous engine had a noise and the cam was wiped out.
The "new" engine has been noisy from the get-go.
Assuming that the current problem is a result of poor assembly (goop in a passage...) may be folly.

Given that both the oil filter housing and the oil pump would be re-used during an overhaul.
I would be wanting to verify both of those valves, before digging any deeper.
BB