[OG68]

The sending unit itself is a variable resistor as are all the gauge type sending units.
Higher oil pressure translates into high resistance.

At 0 PSI - 0 ohms
1/2 gauge reading - 45 ohms
full gauge reading - 90 ohms

Using a 12- 13 volt volt power supply and adding resistance to the circuit should put you in the ballpark.
The only other variable would be the accuracy of the sending unit. To check that you would need to compare against a mechanical gauge