Dear Morgan;
Two things come to mind.
First: Is there a spring & washer on each side of the connecting piece that the oil line feeds?
Second: Is there a small clip/deflector attached to the oil return line at the top?
If any/all of that stuff is missing you can lose pressure there.
Also; Does your engine have solid lifters and what is your oil pressure cold when you first start it?
Good luck, John M....
