If you're going with aftermarket guages and a custom installation, you can generally wire it from what you have and the guages will come with all the proper sending units and wiring info. If you're talking about a "correct" dash conversion, someone else will chime in about their experiences, I'm sure.
The reproduction guage packages(ShiftWorks) etc., have the oil pressure sending conections included(I would not use the plastic tubing, copper instead) and the parts and instuctions to convert the idiot lights.
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