[Lynn Eades]

Kevin, the four digit number is called the Model code.
As examples of 1/2 ton 4x4, the Model code for a WC-27 (this is called a sales symbol)
The 1/2 ton Ambulance is Model code 4139,
A WC-41 (Closed cab) Model code is 4162, while the two Reconnaissance models with and without winch (WC-23 and WC-24) are both Model code 4119.

For 3/4 ton WCs: WC-51 and 52 the model code is 4290 for the Bucket seat body (body work from behind the seats forward) while the pickup body (rear cargo bed is model code 4266. (that was complicated)
The plate with the 4290 is fixed to the front of the cowl just under the rear of the bonnet. (I don't think there was a plate attached to the 4266 on the body)
The WC-56 and WC-57 Command cars (reconnaissance) are code 4219
The Ambulance (WC-54) is code 4239
The Carryall is code 4249.
Any how...
The first two digits would be first year of production of that body type. (1/2 ton were 41 models and 3/4 ton 42 models)

A quick google search tells me that the other number is the body number, or if you like the number on your cab was that many from the start of production (yours was the 33,325 one built) of that Model code.

Sorry I dragged that out.
Lynn.

So, your model of truck was first built in 1942, the body code (for ordering parts) is 52, and it is the 33,325th. body of that type built (1942,1943 or 1944???)