72 318 Scamp. Low oil pressure 1 minute after startup.

I'm not grumpy; I just look grumpy, and since my wife has a headache all the time, I just don't gibachit,lol.

It's not that Mopars have small holes in the pick-up screens; rather the valve seals bake hard, crumble, fall into the pan, and end up getting sucked into the pick-up housing. After the pieces from all 16 get in there, then there ain't much room for anything else!
But that sudden drop with fresh oil has me stumped. It's more like a shop rag is in the pan and getting sucked up.