What to do?

So, I have the oil pressure issue in my 318 that has baffled everyone I've asked. Upon starting it will slowly edge up to 15, maybe 20 psi, then fade to zero as it warms up. I took the car to a local shop, asked them, and they hooked up their guage and told me, "it has pressure when it starts but then it goes to zero" DUH, that's what I told them. That will be 40 bucks, please. They think it's gonna need to be rebuilt, that the bearings are shot. I was told by a couple old timers, though, that the relief valve on the oil pump could be stuck. Has anyone here had the relief valve stick on their engine and what are the symptoms?
I have a guy over the hill in Santa Cruz with a fresh block for me to start all over with, and I am ready to go get it, but something tells me I should look deeper into this issue before I throw in the towel. The person I got the car from installed the engine, and insists he had it open, that it was a low mile engine. I asked him why he had 8 quarts of oil in it and he had no explaination. I bought another 318, it was a 'running' engine, but got it home and the cam bearings were delaminated, destroyed. So, I have a grand total of three 318's that I can't use, and I wanna buy one more? Ha!
This duster of mine is looking at me sadly every time I go into my garage, like WTF big mopar guy? Can anyone help a brother out?