Mike,
Similar problem in my Ford Racing stroked 351 Windsor with 2000+ miles on it. I live in sunny Phoenix and my BDR Cobra has an
oil cooler. With 30 wt
oil at normal operating temp, I ran 25 psi at idle and about 55 psi at 2000 rpm. The engine sat idle for six months while I was making reapirs to the body. Upon restart, I installed a new filter and added 5/30 wt
oil. I primed the engine by cranking the oil pump, not the engine with the starter. At normal operating temp, the oil pressure dropped to 15 psi at idle and 40 at 2000 rpm. I also noted a valve or two clanking at idle when the radiator fans kicked in (at 93 C). So, I drained and flushed out the 5/30 wt oil and replaced with 30 wt oil. Now when the fans kick on, I have 25 psi at idle and about the same 55 psi at 2000 rpm (back to the original pressures).
So, I would take Don's advice and drain out that 5/30 wt oil and replace with with new oil of like kind that was in the engine prior to your internal work. If you are 20 psi or above, you should OK. I would not feel comfortable with oil pressure at idle much less than 20 psi. (There are past threads dealing with oil pressure. You should review them.)
Good Luck. I will keep my fingers crossed for you!
Phil