From the Dodge Pickup History & Restoration guide book:

The 1st "B" = the body series, the "3" = 1951-1952 model year, and the last "B" = 1/2 ton. a number following that "108" would be the wheel base.

Engine numbers covers 2 years indicating there was little or no engineering changes over those 2 years to the motor. (49 & 50, 51 & 52, 53 & 54.)

51 & 52 numbers look like this:
A B-3-B-108 with a motor number starting with a T306 is a 51-52 1/2 ton, with a 108" wheel base.

A B-3-C-116 with a motor number of T308 is a 3/4 ton with a 116" wheel base.

A B-3-D 116 with a T310 motor number is a 1 ton with a 116" wheel base.

A B-3-D-126 with a T310 motor number is a 1 ton with a 126" wheel base.

A B-3-PW-126 with a T137 motor number is a 1 ton Power Wagon with a 126" wheel base. (All Power Wagons have the T137 motor number, an early T137 is a 230 CI, the late T137 is a 250 CI.)


There is no mention of casting numbers, but one might think a casting number ending with a 52 might indicate a 52 model year truck.
This would indicate the 3/4 ton front axle has been added. Gene