According to the LMC Truck Catalog: 10 = 1/2 ton; 1= 116" wheelbase; 22= 228 in-line 6; P= Pontiac Mich. Assembly Plant. Note: their chart states that "1951 models did not use Assembly Plant codes", so you may not have a 1951? Hope this helps!
Doors- vent windows with a twist down handle= 1951
1970 Chevrolet C10 Grandpa's -- My first truck -- In progress to shiny Follow the build in the Project Journal 1950 Chevrolet 1-Ton Dually "Ole Red Girl" In the Stovebolt Gallery More pictures here 1951 GMC 9430 1 ton dually--Shiny! | 1972 Chevrolet C20- Rusty- the puzzle box lid for the C10 | 1962 AMC Rambler American- my wife's Parts trucks- 1951 GMC 9300 | 1951-GMC 9430 | 1951- Chevrolet 1300