The oil pressure issue turned out to be due to the intermediate shaft being installed incorrectly when I went back in to prime the oil system the second time around. I had removed the intermediate shaft between priming sessions because on the first run, it was in upside-down, making it impossible to install the distributor afterwards.
I've attached a few photos, which show that the shaft was not actually making contact with the oil pump, but instead spinning right next to it. I was able to get the shaft installed correctly with the help of my endoscope and holding the shaft with a magnet on a stick. Took a while, but I got it right and was able to verify by spinning the pump by hand using my oil priming shaft, and feeling clear hydraulic resistance.
Here are the pictures in case you're not logged in:
As should be clear now, the moral of the story is: INSTALL THE INTERMEDIATE SHAFT BEFORE THE OIL PUMP!
I actually did try installing the intermediate shaft while installing the oil pump with the engine upside down. However, it immediately fell out, through the distributor hole, as a previous rebuilder had ground the retaining "ears" off the intermediate shaft, and I was not aware that such ears existed. It wasn't until the motor was installed in the car that I realized the shaft initially had "ears" on it to keep it from falling out, and that they had been ground off.
I guess I got lucky the first time around when I installed the intermediate shaft to prime the oil system. Second time around took about 30 minutes, using the endoscope and magnet on a stick.
But I'm just relieved I don't have to pull the motor.
Thanks for all your help! It's raining today, but I should be able to fire the motor up next weekend!
