New to me Barracuda with Mopar Crate 390hp low oil pressure

quote"These are some off brand gauges and the Optima battery is now 11 years old so when its gear at low rpm the volt meter is bouncing and the lights flicker as the electric fan is pulling power. I know that volts can cause irregular meter readings on some gauges. Could the cheap gauges and/or low battery volts be throwing out the very low oil pressure reading? This is my best hope.end quote
Sounds like you have a sending unit type aftermarket oil pressure gauge,use a real mechanical oil pressure gauge.
The fact that its dropping that much though does show a lot of of oil by passing either worn bearings or the roller tappets aren't correct