D=First year of production code “D” is for 1942
U=Body style “U” utility truck (amphibious)
K=Front wheel drive. GMC still uses that on trucks today (K5 Chevy Blazer)
W=Two rear driving wheels (tandem axle)
B is 1940 and C is 1941 date codes that appear first…
A 1939 Model Year
C Conventional Cab Layout
K Front Axle Driven (selectively)
W Both (Tandem) Rear-axles Driven
X Non-standard (Timkin Supplied) Driveline
353 Chassis Code