After discovering my oil pressure gauge is just a dummy light, I want to put in a mechanical gauge. Can I use the hole that my current oil pressure switch is in? I plan on removing the switch and just letting the dash gauge be dead.

 

So, for anyone else who ever does this:
Once you remove the stock oil pressure switch, the dash gauge will be dead.
Stock oil pressure switch is behind the dipstick, it has a wire coming out of it.
I had to use an adapter, however there was one included and my line fit perfectly.
Invest in the copper tube. Don't use the plastic one.
Be sure to run the truck and let the line fill before tightening it down. It'll make a small mess, but if you don't the gauge won't read correctly.
From what I've discovered driving around in 80 ish degree weather:
Cold start: 50 PSI
Cold idle (1000 RPM): 50 PSI
Cold run (2000 RPM): 50 PSI
182 degree idle (750 RPM):15 PSI
182 degree run (2000 RPM): 25 PSI
182 degree acceleration (3000 RPM): 35 PSI
If any of these are inaccurate someone let me know. This is 5W-30 Conventional, fresh, 80 degree ambient temperature, 4.9L engine.
If anyone would like pictures PM me.