I have a lifted 1979 F100 that someone put a D1VE casting engine in, which has an Edelbrock intake and Holly carburetor, and brand new headers. It has a 3 gage set under the dash with temp, voltage, and oil pressure.  It was rebuilt as a 429 to factory specs by Jasper around 2014 and has only 3000 or so miles on it since then, so it has sat outside for months at a time.  

Recently the dash oil light came on. I took it to a local mechanic Ive used before with success and they said it needed an oil pump.  They changed the oil pump but still no oil pressure. They bought a new oil pressure gage to see if their equipment was the problem with no luck. They said it has "volume but no pressure" They were running out of ideas and next step was going to be to pull the engine and check for clearances and said they've had some issues with Jasper engines on occasion.  Thats going to be thousands $$ so I told them to wrap it up and ill just take it home and see if I can figure it out--ill drive it until it blows up before I spend thousands just "looking" for a problem on a practically brand new engine. I drove the truck home, about 1 mile. It had been idling the day before well over an hour.

I bought a mechanical oil pressure gage and hooked it up last night to the oil sensor location behind the intake. Zero oil pressure. Had it running until temp said about 195, still zero, needle didn't budge.  Id rev it up some maybe to 2000-3000 RPM (i don't have a tach) but nothing.

Confusing part is I saw on your old oil pressure sending unit post, it says if there's really no pressure the engine would be making all kinds of racket--it doesnt. Another thing I read somewhere random was an engine only lasts 30 minutes before its basically trashed with no pressure.  But this truck idles fine no crazy noises and so I just dont get it. 

I've read to check and see ifnyou can see the oil pump shift if you remove the distributor. Ive also read the pickup tube can crack. Ive also read the oil pump if not primed right can be at risk of not working. Im about to be off work the majority of the month and id like to be able to use the truck for some huge home projects im working on. I have around $10-12k into this truck but it looks like junk so I don't want to sell it.

Any suggestions on what is the most common problem on this?  Or the first things to check? Should I just drown the oil pump to try to retro reprise it? Or just maybe pull the distributor first? If I pull the distributor what is the risk I knock the oil pump shaft into the pan just from doing that?

Side note, I 100% agree with you on Lexus and Toyota reliability posts, my daily driver is a Lexus ES300, love it!