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

Unless you have really examined the whole system and looked to find the most limited restriction, there is no way to know. The stock oil interruptor limits the flow to around 5% of the time (and less at very high RPM's), and lowers the rocker shaft pressures to a few PSI anyway. The H-S statement is unqualified so has to be taken with a grain of salt IMHO: Is it for the stock oiling system? Or for full flow cam bearings? What size is the flow restriction where their rocker shaft sits on the stand with the bolt going through it? It can be very different from the stock restriction at that point, smaller or larger.

If you read the Comp site tech info, you will learn the completely wrong info on the geometry for this system. So I am just advising to be to understand the system rather than take everything at face value.