Opinions sought on odd engine knock

Thanks for all the input. Odd cylinder ... nyuck, nycuk, Curly Joe. Guess I walked into that one....

Using WIX or Hastings oil filters, so no joy on that simple fix.

Tming chain was changed due to trying to eliminate a low pitched rattly sound in the crankcase (as well as get rid of all the chain slack) but that rattly sound is still there (different sound than the knock). No change in that sound, and that is also concerning; it remains after a process of sorting out noises and eliminating the water pump bearing noise, the 3 exhaust manifold leaks, worn timing chain noise, etc.

Yes, a mechanical lifter cam; this is definitely a lower end knock, not a valve train tap. Main bearing? I HAVE heard that once but it was really bad.... as it tends to be when the main webs crack.... that was a bad day.

Compressions all in the 115-130 range. Reluctantly, I think all the ideas to tear into this are probably the best; I was starting to think the same as Redfish: no need to allow something to keep eating up the insides. I've been trying to keep this car as original as possible, but looks like I gotta get inside and flush this one out. Sounds like time to at least pull the pan and then probably the head..... BRRRRR!

Many thanks for the input. And I'll keep in mind that a greasy day under a hobby car is better than a clean day working.