The issue is whether the gauge will be used to indicate fuel pressure, which is what the dial in the original car was doing or whether you want to change it to a fuel gauge like in a road car, which is what flyingsaucer is suggesting. Personally I doubt whether fuel pressure is meaningfully modelled in AC (no idea, just guessing) in which case I would get the fuel pressure gauge to mirror the oil pressure, perhaps with a slightly modified scale so they don't exactly match.
That forum page and wiki are very helpful I agree. On the CSP page, OIL_PRESSURE is a recognised input and I imagine you can have two oil pressure dials.