I'm the guy in Hawaii. Check out my thread "rebuild, now no oil pressure". Did you put on a new timing cover (the high volume type?? Check the gasket between the timing cover and the thrust plate. I found that 4 out of 6 that I had in the garage wouldn't work correctly. It's hard to explain, but there is a portion near the suction of the pump that most of my gaskets have a cutout (for no apparent reason but to save money on material) which doesn't allow the thrust plate to seal correctly. I found it when I took the thrust plate off and look closely at the gasket. There was a small portion I could tell wasn't actually sealing as the timing cover didn't have any mating surface there. But your symptoms sound VERY similar to mine. I could get initial oil pressure and then it would drop off and go away. Then I would re-prime it and same thing. It was because the oil pump was sucking air in through this gasket area. I hope this helps...
If you want, I can probably take a pic of the two types of gaskets and send it too you. That may make it easier to see.
Derrick