No, oil pressure sender.

I've had two oil pump failures: One when the pump tried to digest
shrapnel from an engine explosion and one from a twisted oil pump drivershaft. (both traditional Pontiac V-8s)

I seriously doubt the oil pump'* bad. Look elsewhere first.

Looks like I need a motor. When the tech who worked on my car grinded off the old gasket...tiny shreads must have fell down below and ruined the bearings.
I used to work for a salvage yard. they have a motor there and will install it for me. They guarantee their work as well as the motor.
Should I replace anything on this used motor right away upon the installation?

Yes, it can. My 1993 had the oil pressure check valve stick open I think it was. The oil pressure shot up, blew the oil filter off, then dummped all the oil pressure due to there being no filter. Unfortunately, when this happened, the previous owner didn't shut the car down fast enough, and it took the motor with it. We replaced the pump and had it running fine when I bought it until we took it for it'* first test drive. 1 mile down the road it started knocking like an SOB. Yanked it and put a 28k motor and and she runs like a top.

Good luck with the car. Hopefully the new motor will get you up and running soon.

sounds like what happened to my car the other week. got off the highway after a 5 and 1/2 hour drive and car started knocking all of a sudden. looked down at the oil pressure at the next stop light and it was in the red just above 0. the engine had thrown a rod bearing and cracked the block......only 82,000 miles on the car. now I have a rebuilt motor in the car and runs great. the previous summer the coolant light had started comming on and off and turns out I was supposedly leaking coolant out because the UIM had cracked.

in a used engine i would put all new plugs in it, look for any visible oil leaks, if any, re gasket while its out of the car.

Will do.....
New plugs, wires, t-stat, pcv....

i'm gonna keep the SC off my old motor and keep it as a spare. it still worked great...no sense in trashing it.

I would also suggest replacing the rear main seal in the "new" motor. Even if it'* not leaking, it'* good insurance. Changing it in the future involves pulling the engine.

Okay, I'll get a rear main seal from my work and have em' put it in.
The motor is out of a 93, so I'm good to go.