67 Barracuda oil pressure gauge

I dont have an answer to your direct question, BUT I would not trust 50 yr old gauges. We have our factory gauges installed, BUT a set of AutoMeter triple gauges mounted under dash. Oil psi, coolant temp and volts. We mounted them under the dash and look perfect.
Get an aftermarket oil gauge and hook up under hood to verify.
Good luck.
Spinning the oil pump with a drill, then rotating the crank about 3”, then spinning the oil pump some more. I’m doing this by myself.

I can turn the key on, spin the pump, and the OP gauge is now moving. I can tell because the pressure is bleeding down when I get out from under the hood and look at the gauge.

Which leads to the question, “What do the increments on the OP gauge mean in pounds of oil pressure?