The older oil pressure sender uses the same thread as the later oil pressure switch, so swapping is easy. There's just enough room for it to fit. See this pic:
http://www.supermotors.net/vehicles/registry/media/281470
Instrument clusters after ~98 have an oil gauge that's permanently faked-out internally, so this swap can't be done on them. You can only convert it to actually work if you can see a resistor in the oil pressure trace on the back of the cluster. If the trace is solid, then the resistor is built into the gauge head. You might be able to swap out the gauge head...
