I did not have the engine running when pressure testing. Per your suggestion, this morning I filled the three core plug pockets with oil and re-pressurized to 7 psi - still no air bubbles or coolant leak. I then proceeded to drain all the new oil I had just filled it with and then drop the oil pan. I would estimate at least two cups of water/antifreeze poured out the drain plug before uncontaminated oil started to flow. Next, I again pressurized the radiator and looked up into the engine to check for leaks around the cylinder sleeves - still nothing. Now I am thoroughly confused! - how can it be that after changing the oil, driving it back into the shed, and then doing various pressure tests that I could accumulate two cups of water in the oil pan and now when I pressurize the system with no oil pan attached that I see no coolant flowing down into the open cavity where the oil pan would be? Please forgive my ignorance as I'm a novice at engine work, but I thought that regardless of the leaks location I would see antifreeze drain back to the oil pan. Any advice? Do I need to pull the head next and inspect the head gasket? Thanks again for any advice!