Have not heard anyone talk about what kind of oil pressure you are running at now, at startup and after warmed up. 5 psi oil pressure at idle is not enough although better than Zero. Sounds like a lot of valve train noise in the video, that is the first thing that shows up when you are experiencing low oil pressure.
What does the oil look like when you pull the dipstick and wipe it on a white paper towel. Black and Grainy or clear like brand new oil ??? Next pull the oil filter and cut it open, you can zip around the base of the oil filter 1" up from the bottom and let the can fall off. Have a drain pan there to catch everything that comes out of it, then you can see what it has trapped out of the system before it sends the oil though the engine again. If that filter starts plugging off it will reduce your oil pressure.
Also take a magnet to the paper filter from the inside of the filter to see if it picks up any steel from parts wearing out. Seeing steel slivers in there is not a good thing, and there will be some black sludge in there too.
Can drop the engine oil out too and see what comes out of the pan.
Put fresh oil and a new oil filter and fire it up again and see if things quiet down a bit. If all checks out OK so far but still making noise, you can add 1/2 pint of Lucus Engine Oil Treatment to the oil and try again (the thick stuff like Honey . . like the STP) this should quite things down a bit as a test. Will help you determine if it is internal engine bearings or valve train, or an external item like a cracked flex plate at your torque converter.
Still have not heard that you have checked out that mechanical fuel plump yet, they will still pump fuel with the arm going loose inside sending the noise and rattle all the way down the camshaft and up through the valve train. Just think about the "Beat" of your knock, it is not like a sound that all 8 rods are slapping at the same time. It's is more like a single "Beat" of the Eccentric on the cam hammering the loose Plunger Arm on the fuel pump sending the noise down through the cam and into your block.
Can also pull the distributor cap off and see how much left to right turning distance you have on the distributor rotor. More than stock distance travel when turning left to right tells you things are getting wore out down below there, all the way down to the oil pump and distributor drive gear and bronze bushing in the block.
