To update to 12 volts, the only gauge to worry about is the fuel. A simple resistor is all that is required. http://www.speedwaymotors.com/Runtz-12-Volt-to-6-Volt-Reducers,2374.html
Oil pressure gauges can be updated by various venders to read higher pressures. I have been using the stock 30 lb gauge for 17 years now without it blowing up! I have no idea how much pressure over 30 my engine makes, don't really care, as long as it makes pressure.
Amp gauges don't care about voltage.
Temp gauges can also be upgraded to longer probe tubes and zeroed out needles.
Speedometers generally just need cleaning and new decals. Decals are cheap and easy to get from most any of the venders in the links section above. Cleaning is pretty easy if you take your time and work in a well lit area. Its also a good time to zero out the mileage. Missouri had no problem with me starting from zero.
Ask Alvin Paris,http://www.stovebolt.com/gallery/parris_alvin_1937.htm , there is a Datsun 280Z or 240Z dash setup that pretty much bolts in, but it to is getting old.
Joe
