The
oil drain trays return
oil to the valley evenly front to back instead of just at the front and back of the head. Originally the FE's were all solid lifter engines with NO
oil to the tappets so this spread oil out over the tappets and bottom ends of the pushrods.
The oil to the top of the engine is fed up by #2 and #4 cam bearing area to a groove over to the headboltand then to the rocker shaft stand--these grooves used to get sludged up with poor oil change habits, and then excessive rocker arm, valve tip and because of low supply, the low drain back killed off tappet rotation, then cam lobes,etc.
A common way around the plugged up supply was a set of steel lines that went from the oil pressure port up and under the valve cover and into the end of the rocker shaft. This was a system actually patented by a friend of mine.
Your pics show that your shaft assy aren't set up properly as the washer/springs are not installed in all locations and I would even bet that the shafts are upside down---those rocker arms wore severely with higher lift cams and springs over the valve tip which was a source of noise when they would slip sideways over the valve tips--also the clearance of the rockers to shaft needed to be oiled pretty heavy to prevent wear, insure that oil went to valve tip and pushrod . In the old days noone ran 10 wt oil in these engines--it was always 30 + and the pressure in the FE was so high that they relieved the oil pressure at the end of the system--the spring in the pump relief was just to prevent filter blow out on cold starts.
Your car has several problems---I would suggest doing the bottom end to correct oil pressure problems, and get a set of Erson type roller rocker set up to bring the top end up to modern standards.
IOf you will run the engine with the valve cover removed you will see that you don't have any oil and you can then pour a can of oil over the rocker assy and see that the noise goes away--
By the way you should be wearing earplugs driving a Cobra, not a stehoscope!!!!