Are we talking electrical or mechanical gauge?
I'm assuming electrical. I installed a prosport oil pressure gauge in my 6 and it came with the gauge and an oil pressure sending unit. So you ran wires from the gauge to the sending unit.
Anyways, I installed it by making a custom T using brass fittings and teflon tape from the hardware store. The T setup allowed me to have both the stock oil pressure unit (for the dummy light) and my prosport sending unit hooked up at the same time, thus avoiding CELs.
I did everything during an oil change so the oil was all drained. I took out the stock sending unit and attached a small piece of pipe straight out. Then on the end of that I attached a T fitting. Then on each end of the T I attached the stock and prosport pressure sending units. It worked well for me.
So, you'd have find the stock sending unit and see what the space around it looks like to potentially find something that works for you.
Also, as Jay mentioned, you could use a sandwich plate, but that would require you to switch to a spin-on style oil filter as the stock Speed3 cartridge style filter setup will not work with a sandwich plate.