Oil temp gauge in the rally bug is actually reading three different senders. The rotary switch to the right of the gauge controls whether I'm reading of the 'E'ngine, 'T'ank, or 'F'eed (post oil cooler) sensor. The wiring for this is relatively simple, and could easily be done with a pressure gauge with no trouble. You will need to test each of the senders to correlate their accuracy both to the temp/pres you're measuring and to each other. My three oil temp senders, for instance, are off by a total of 10deg from each other when measured in boiling water. Once i figured that out, it explained why the temps "in-car" weren't matching up to what I expected.
-Dave