I know this is a bit old, but there's almost no correct information in this entire thread, and since it came up on google search results I registered just to clear some things up for any other CUCV owners out there who get confused and run across this.
The glow plugs are 12v. Seriously, 12v plugs.
The glow plug _system_ is 24v. The resistor bank mentioned is _only_ for stepping down the 24v supplied to the glow plug system 12v, so the plugs get the right voltage across them. If the resistor bank shorts out, you just double the voltage going to the plugs. That's probably how you'd overvolt the plugs, not by simply installing 12v ones. You're supposed to do that. You can read the TM to troubleshoot the entire glow plug system step by step.
Besides the starter, the only other 24v things in the truck are all military things like a possible military radio. The bus on the right next to the back seat is 24v, and the bus under the hood behind the back battery is 24v. Nothing much runs off these though, certainly not the civilian parts in the car. Those are all regular old 12v. Every 12v device in the car besides the glow plugs are powered only by the front battery, so it's under a heavier load most of the time than the rear one, which really only gets used for starting. Rotating batteries therefore is recommended.
Follow the wiring, there is a run from the front battery positive terminal that runs to another bus on the driver's side of the firewall, it's smaller than the big 24v buses but runs power to most of the civilian items in the vehicle. The ground for both 24v and 12v items is the chassis, since the batteries are in series. The rear battery, passenger side alternator has an isolated ground that returns only to the negative of the rear battery.
So, you can use the Wellman 070 plugs, but make sure you get the right spade connector, CUCVs and other 6.2 applications have had different glow plug connectors. You can convert the entire system to 12v, but then the military TM manuals no longer apply and you're on your own for support. If it is still wired stock, read the TMs! No need to go to a base for part numbers, etc, they're all in the manuals.
Cucv Wiki - Steel Soldiers::Military Vehicles Supersite
Sorry bout using that little image at the start of the post too, but I'm new to this forum and it just fit so darn well. I'm gonna go back to working on my CUCV now.