Low oil Pressure Please help

[oneloweffie]

ok so here's my prob I have 5.0 I picked up for my F-100 pickup I am not sure what year the motor is. I do know its a roller cam! I was told maybe a 96 cougar was the car it came from. it was a full engine with the EFI at the time I picked it up. I bought an Edlebrock performer 289 manifold and carb and a Pertronix Flame Thower Dizzy from a local speed shop. everything else is stock!! the motor was clamed to be rebuilt when I got it. ok so I got everything put together and installed into my truck..and the motor starts and runs but I get very low pressure..I have VDO sender and gauge. now keep in mind everything here is brand new parts wise. the pressue shows a tad above 0 and about 20 Psi at about 2K RPM. I bought a 13 dollar mechanical gauge it came with white nylon tubing..and I can see the oil climb the tubing about 4 inches worth at the 2K rev. and it goes back down when idle. but still shows no pressure. I replaced the oil pump with a brand new stock...I changed the oil and Filter and used my drill to prime the pump (ran for about 2 mins) when I saw oil flowing down through the Dizzy hole I figured it was enough. (just an FYI I did the priming thing before I started this with the old pump also) put back together and nothing..still the same problem. and I am also getting noisy valves. so with all that said can anyone think of somthing I missed? should I be running a hi-flow pump? is this motor junk? I know its not a mustang but I figure ask the pros!!! thanks for all your help