Need a new oil pressure gauge

[Skunksmash]

My old oil pressure gauge is finally going kaput. I've got two new sending units on the engine, so I doubt its that. The gauge has always been kind of flaky, but now its acting like its knocking on death's door. My oil pressure really isn't something I want to leave to chance, so I've decided to replace the gauge with a good aftermarket one. So:

1. What size are the oil pressure gauges in these old trucks? is it 2.5"? I ask because sometimes accepted standards aren't the actual measurements.

2. Given the 3 wire (or was it 2..) nature of the oil pressure gauge, am I looking for a "mechanical" oil pressure gauge, or electrical? Not too sure on that one.

3. What numbers should I have on my gauge? You can get a lot of different types of gauge faces with various numbers depending on your application. My engine is a 350 TBI. What should be my lowest, medium, and highest numbers on the oil pressure gauge?