The only gauge on your truck that's electrical is the fuel level, a voltage reducer will take care of it. To extend the bourbon tube on the water temp, BOW TIE BITS used to do them out of Wichita KS. Jim Carter likely knows someone that does it if they don't do it themselfs.
The speedometer can be cleaned as DIY project if you take a little time be careful with it. My '37 works really good with just a cleaning, it's going on 90 years old now. I calibrated it using a variable speed drill motor I set it up in a vise. Using a hand held mechanical tachometer used for small engines, I set the drill to 1000 rpm. 1000 rpm is the industry standard all speedometers are set to to read 60 mph. With the drill at 1000 rpm, the speedometer read 70 mph. I simply pulled the needle off moved it and kept trying till it read 60 mph @ 1000 rpm. At slower speeds its slightly off, and above 60 its slightly off, but neither is off so far I will get ticketed. I don't even notice it being off, I mostly follow traffic speeds anyway. Odometers are gear on gear driven, they will always be correct providing the input rpm from the transmission is correct. The speedometer needle is magnetic driven, and as long as the magnet is still good, the speedometer should work as long as its clean and lubricated.
Amp meters don't care about voltage, the amps, and amps is amps no matter the voltage.
Oil pressure is mechanical, a good cleaning and lube is all it needs.
New decals are available and are easy to apply.
