I didnt listen to the vids but another thing to possibly consider is a cracked piston skirt.

I had a BB mopar I did when very young that I got pretty aggressive on putting in the pistons and from day one it had a knock like described.

I would run it very very hard and it never broke till a drunkin (I was really young) night of running through town in low gear at 5700 for a long period when the skirt let go and I had a smoker that was an easy fix.

Is that a cam bearing that also feeds the mains? If so what if you have been running bearing material through things or partially blocking things?

It sounds like you have a nice setup going and although im overly anal at times id be pulling it and inspecting things very intensely to the fix.

One would think it would be semi easy to find all the issues on tear down.

But whatever the case I hope you resolve it without further damage.