It's ALIVE, sort of.

Just had this exact problem last Saturday with a 360 I helped install in a truck. The oil galley plug was missing from the left bank and none of the lifters pumped up on that side. We did have oil pressure when we primed it but it came up VERY slowly and only to about 15-20 psi. Once the engine was running it only managed maybe 25-30 psi @ 2500 rpm. I'm pulling the intake tonight to put the plug in place.