Thank you for the nice remarks. I'm fairly sure that I've established that the yellow is a repaint.
There's more to the mystery: two data plates are brass-riveted to the driver side kick panel. While the plates show "Truck, 1 1/2 Ton, 6x6, Personnel Carrier," I can find no WC 63 identification or serial number tag. There is nothing on the glove box door.
The yellow paint did not seem to have been a repaint because the components and cab would have had to have been removed to be painted. What I mean is that floor panels would have had to have been removed to expose those areas for paint. Nevertheless, they have been painted completely and professionally. I've attached more photos.
The serial number stamped on the frame--82041004--indicates a build possibly in early 1945.
To make matters worse in this admittedly obscure history rabbit hole, the truck was modified with a rear step bumper and hitch assembly to accommodate a standard ball hitch (removed from the truck before I took the photo). This was no bubba modification; the bumperettes were removed and a professionally fabricated bumper installed with the pintle hitch receiver relocated as shown in the photo. The installation was accomplished without welds or drilling extra holes in the frame which allow a simple return to "original." Here there is also evidence of yellow paint on this modification.
The body data plate screwed to the body just aft of the cab on the driver side solved the mystery (I think). It was painted gray over yellow indicating two repaints. Note the olive drab ghost left behind after removal of the data plate.
Because of the truck location where I purchased it (Hesperia, CA) and its proximity to Naval Air Weapons Station China Lake (about 100 miles) along with the key tag, could it be that the Navy acquired the truck for use at the NWS China Lake? That is, could it have been used as an airfield "Crash Truck," retired from that use, repainted gray, remained in service for some time, then surplused? Likely or unlikely?
Then there is the issue of the arctic cab. That piece is the original gray without yellow underneath. It makes sense that the Navy fire station would have desired a hard cab for airfield rescue and recovery. If so, why not paint it yellow, also? Or, perhaps, they acquired the cab, left it gray, then subsequently repainted the entire truck gray over the yellow.
There's more, but I'd like to hear from my fellow collectors. Thanks for reading, John
