I don't know if this will work, but if you are looking for a possible solution, you might be able to use the later style oil pressure gauge from a truck or suburban. My 89 suburban (below) has one of the electric units, and that is a fairly common swap for the volt gauge.
If you grab the oil pressure sending unit off the newer engine, the block should be the same, so it would just be a matter of connecting up the wires and tapping into power off the rest of your gauges.
