Oil Pressure

I picked up an engine from Merv Adkins that was rebuilt some time back and never run in a car. He ran it for me and it had great oil pressure but after dropping it in the oil pressure on the instrument cluster barely reads, and then only at high RPM. I checked the gauge by grounding the sender wire, and it works fine. The lines to the oil filter canister are clear. Another baffling thing, the engine starts great but stalls only when I come to a full stop and is hard to restart. Still, great to have a 12 back in the jalopy.

Could it be the oil pressure sensor?

I agree it's probably the sending unit next to the filter cannister. Finding "good" 50# sending units might be hard so you may end up using a 80# unit and while the indicated pressure won't be accurate at least you'll have a better indication of oil pressure. Engine stalling: by being hard to restart a "warmed" engine do you mean the engine cranks slowly and laborious? You may have to set the idle up a bit until the new rebuilt "snugness" subsides.

You were right about the oil pressure and I solved the stalling mystery. Fuel pump pushrod isn't long enough - or fuel pump is worn. Put a 1/8" spacer in the fuel pump cup that receives the pushrod and all is good. Merv said he ran the engine in pretty well on the stand. It starts on the dime whether it's cold or warmed up.