Sam,
I do have literature on Truxmore conversions. They did do things like adding an inner frame liner on top of the other 2, torque links, trailing axles, etc. Their parts were installed at authorized distributors. So, if the truck was shipped from Ford to a truck equiper for beefing up, they must have sent them out with the blank GVW plate. Similarly, I have had a couple Marmon-Herrington 48-50's that had the prefix left off of the serial number on the plate. I'm sure that was because they knew that M-H would be assigning their own prefix on their own plate. I have no doubt that your truck was built up extra heavy like you say, but the truck in question doesn't appear to have much done to it, so I'm still baffled as to how they justified that drastic of an increase in GVW.
You have quite an impressive fleet of trucks. All of the 48-50's are gone? Do you happen to have any 337 flathead parts? I'm in desperate need of a RH head with the bypass port in the front.
Chuck