Here's an embarrassing video of the motor in its alternative state of operation. Did my best to capture the horrible noise it is making. I show the oil pressure gauge fluctuating and the rpm's correlation. No those are not the orginal 'Cuda doors gutted. They are my spare race doors.
Ok...so you’ve eliminated the fuel pressure issue.
It certainly is missing on more than one cylinder. Usually if you stick a valve it gets bent, especially the exhaust valves. Doesn’t always happen, but it usually does unless you have a mile of P/V clearance.
While you have the heads at the shop (or maybe before you pull the heads) I’d take the oil filter off and it it open and look at the guts of the filter to see if there is any junk in there, and if there is how much and what it is.
Just off the top of my head...if the engine has metal from the first cam floating around in there, that junk will end up in the lifters and it will affect lifter function. Although, even with my ear buds in I couldn’t hear if the lifters were clattering while it was missing. That is due to 35ish rock concerts over my lifetime and literally standing on the starting line for thousands of unmuffled passes. So it could be making noise and I can’t hear it.