For the voltage regulator, those electronic hobbyist on the list should be able to make a simple replacement.
LM317T (T0-220 package)
R1 (out to adj pin) 220 Ohm
R2 (adj to gnd) 1200 Ohm
Diode (Voltage to in) IN4007
input cap 0.1ufd (disc 60V is fine) output cap 1.0ufd (tant. atleast 10V)
For the circuit, look at a LM317 datasheet. Check the LINEAR Databook's (Motorola, National Semiconductor, etc). The diode just prevents reverse voltage spikes from damaging the regulator.
Mount the heatsink tab with mica washers (pin 2 is connected to the tab). Output voltage is apprx 8V.
Note: I think the system, as a whole, was temperature compensated. The electronic regulator may cause the gauges to read a little higher when it is HOT outside (haven't investigated this).
Everything should fit back inside the original case, keeping a stock appearance.
For thosee who are NOT electronic hobbyist, it is still much simplier to replace the OEM unit with one from NISSAN (about $13).
[with thanks for those supplying notes and current readings]