If you bent a pushrod and threw a lifter out of it's bore you will lose all oil pressure. Pull both valve covers and make sure all the pushrods and lifters are in place.
I had that happen to me, I think I torqued down the rocker shaft too quickly on a filled lifter. Not like I was winging it up to high RPM or anything, heck I was leaving the doctor's office with my daughter when I lost oil pressure.
I also had a very small chunk of casting flash break off in a 360 and get caught up in the oil pump, locked it up and snapped the end off the drive. Not even sure how it made it past the pickup screen.
I had a small piece of aluminum from the rear main cap seal holder on one of my old 426M.W. stocker motor break out when I used non stock oil pan bolts in it, that small piece of aluminum got suck up into the oil pickup and through the hole in the center of the screen under the baffle and into the pump locking it up twisting off the shaft at the old Firebird, now Wild Horse raceway in Phoenix, AZ many years ago back in 1988
I thought it was caused at first by thick oil, it wasn't. I had to take the pump off and apart to find that piece stuck between the rotors after having it twist a new one off as soon as I started it up, stupid me for ASSUMING it was cold oil that caused it
Every stock Mopar oil pickup I've remove the baffle from has that hole in the screen with a steel ring crimp onto the screen to hold the hole open
