I did have a 350 that wore out the thrust bearing on the crank due to a ballooned converter, so much that a crank weight tapped the block at idle. It disappeared with any rpm increase. OP was normal.
I've also troubleshot down low noises despite good oil pressure. In both
cases that I can recollect, the root cause of the knock was a bent/twisted
connecting rod.
In the first case a recently purchase truck had a sound
similar to the OP's video. But at the same time oil pressure was within limits?
After removal & subsequent teardown, it looked like the PO had suffered
a hydraulic lock (due to a head gasket coolant leak) into 1 cylinder.
The head gasket had been replaced, but the reciprocating assembly was
left as-is? And while the engine more or less ran on all 8 cylinders after
the head gasket job, but this one cylinder was noisy similar to the OP's engine?
In the 2nd case, the rod was twisted, and because of new stresses induced
because the wrist pin was working cocked, the piston slap had become
authoritative, and was present cold or hot?
Weird things can be hiding inside an engine, especially when it comes from
the used car manufacturing plant. The previous owner's 'good enuf' is now
your new baby's WTF?
Q: Was this engine ever quiet for you? If so, did it come on slowly over time
or did it suddenly appear? Or did you buy it for the right price with this
noise evident? This might help us narrow down the possibilities...