Just wondering why you say this, I believe that electric gauges are strongly preferred. If you get a broken connection between the gauge and the pressure sender on an electric gauge the gauge will read 0 (or short to some other silly reading), you stop the car and later sigh relief that it's just a simple wire fault and your engine is fine. Also easily repaired.
However, with an oil line going from gauge to sender not only do you increase the risk of an oil leak (engine failure or fire risk from hot exhaust etc) but depending on where the gauge is mounted you run the risk of 120°C+ oil going onto the drivers face/body in a leak at the gauge.
Just wondering your reasons for avoiding electric gauges as it's the first time I've ever heard of that - sure you have a valid reason
Oh and my advice would be to put good oil in, fit a gauge and see how you get on first - It might be in your application (climate, run time etc) that you can get away without one.
Cheers,
Dunc.