A mechanical pressure gauge is a good idea as robs91fox stated. Although, from the past 4 Fox's I have owned, I could say that 99.9% of the time I had oil pressure issues was from a faulty pressure switch. The switch is unreliable, not the gauge.
Granted anything mechanical would be a direct reading and there would be no wires to lose resistance, which could result in erronous reading. But, the benefits of installing a mechanical pressure gauge vs. the cost is just not there. Ford designed it that way, and Boeing relys on electrical gauge indication 100% on all their jets (i know we are talking about cars, but same principles still apply).
It's a personal choice on whether to go mechanical vs. electrical. They both work as advertised.
Do you know if the engine was rebuilt recently? If so, it's common for builders to forget the galley plugs under the manifold. If the plugs are not installed, or installed improperly you can get a low pressure indication.