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

First, get some valve covers on that thing that have baffles in them. If you can A) See the rockers through the fill hole, B) pushing oil out the crankcase filter, and C) plugging up your PCV valve; there obviously aren't any baffles in the ones you have now.
Second, get some thicker oil in there- 10w30 or 10w40. Then see how your oil pressure behaves.