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My guess would be worn mains and rod bearings.I have heard of guys using high volume oil pumps to cure this problem but to me this is not a cure but a bandage til it can be fixed properly.
Have you checked it with a mechanical gauge? What are the actual pressures?
I had a 71 351C that would not die. It held about 5lbs of pressure at idle and 20 wide open. I couldn't blow it up.
After 2 years of hard driving, I finally tore it down and found a main bearing that had overlapped about 1/2". It really was Ford Tough.
If the actual pressures are low, my guess would be worn main bearings.
If it doesn't knock, I'd drive her till she blows.
Or, you can tear it down and install a crank kit and other required pieces to rebuild it.
Jimmy
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