yet another oil pressure thread

[davecarney2]

6.0 swap into my 59. I tapped the "block off plate" above the oil filter to put a sending unit in. I primed the engine. then I started it. zero oil pressure. another thread before was i had a fuel injector issue dumping fuel. soaked the oil so i changed it. still no oil pressure. verified my gauge, even put a mechanical gauge into the block off port. with the block off port open i can crank the starter and get a little flow of oil coming out, when i put the gauge back in and start the motor the needle doesnt even move at all. thinking pickup tube oring since the pan was changed just throwing me for a loop that it doesnt have at least a few psi when i know cranking the starter some oil comes out.

Is there somewhere else i can install the mechanical gauge to verify before i start ripping into the engine? ive watched a million videos so if assuming oil pickup o-ring or the pump. anything else that would cause zero oil pressure?