I would make sure those push rods are open, could have been damaged or got something plugged in them. A 360 magnum has roller lifters, with a retaining plate, how did the lifters "pop out"? Are you using a non roller cam, with AMC lifters, in a magnum block? What year engine do you have?
Just a little more information:
The class I run this engine in does not allow for roller cams. I have been running magnum blocks with solid cam / lifter combos for years. I am using the AMC lifters in the magnum block with a solid cam.
When I changed the lifters, I changed three of the pushrods that are new. I can check the pushrods, but I don't think anything is blocking them.
I called the lifter company and didn't get any useful information. I asked them if I was priming the engine and took a pushrod off if it would oil shoot up from the top of the lifter and they said yes. Meaning - It doesn't require a pushrod pressuring it. No oil comes out of lifter while priming even if I move the lifter up and down in the lifter hole.
Does anyone have a good oiling diagram for a magnum block? I need to see the exact pathway the oil takes from the pickup and the diagrams I have seen are pretty horrible.