The problem: On start up, oil pressure would show 20 PSi. On hot idle, it would show 20 PSi. When revving hard, it would rise to over 60 PSi.

The theory: The pressure relief valve was stuck partially open, allowing oil to bleed at all times, but not enough to not let the pressure rise when revved.

The mission: To strip, inspect and fix the oil pressure relief valve.

The conclusion: After having to remove the engine mount, and skinning knuckles on sharp zip ties, it was discovered that the PRV was in fact assembled upside down!

Reassembling the PRV was a bit harder, as the spring didn't want to let us screw the cap back on - but on start up, now there was no oil pressure!!! Kill the engine, call it a day. I suspect the plunger isn't home, I will check that tonight...