I did not read the whole thread so if this reply duplicates what was said then please disregard.
Did you fill the cooler before hooking up the lines?
What size lines? -12?
If so and the cooler was empty it takes a bit to fill and come around the system that might have an air pocket. Only maybe and certainly not for 2 whole minutes.
The easiest may I know without wiping out the motor would be to pull the distributor and put a drill on the
oil pump and run it up. If you still have no pressure, back to the drawing board.
Hey, did you flush the cooler before installation? Even though they come capped off, that does not mean it was clean and free from blockage.....Steve