Oil pressure fluctuating at idle

[Dead Parrot]

Easiest is valve cover off and engine running. It WILL be messy! Do one side at a time. Check for all rocker tips moving about the same amount. If one isn't moving much, that is your suspect.

Might cut open your oil filter and check for metal bits. Not definitive as a bad lifter doesn't normally make many metal bits and a worn cam lobe might have failed before your last change. If you find a bunch of metal, something is failing.

What is your idle speed? A stock SBC will often idle smoothly well below the recommended idle speed. Too slow can show some oil pressure variations.