Quote Originally Posted by AdmiralSenn View Post
See if you can borrow a proper mechanical oil pressure gauge and hook it up to the gauge sender port. That'll tell you for sure what your pressure is.

I had to do this when my pressure dropped to zero. It turned out that the last person to work on the engine used DELRIN to balance the pistons, which fell out after 20+ years and collected in the oil pickup tube. Almost lost the motor. It survived because the oil was brand new and I added another three quarts on top of that to make it home.

Since you said they had the oil pan off I wonder if something got stuck in the oil pickup and is blocking it. That might cause what you're seeing.
The pressure test went well and it's within specifications. So that leaves the sending unit as the most likely problem.