I know it "SEEMS" like the cab and everything else should be bigger since you are going from a 1/2 ton to a 1.5 ton. However, I am inclined to agree with Bob on this.
The only difference, (I am hoping) is the larger wheel opening, for the 20" tires vs. the smaller ones.
Timmer

If at first you don't succeed . . .
er . . . then skydiving may NOT be for you!

1946 Chevy 1.5-Ton Flatbed Completed
1946 Chevy 1.5-Ton Just getting started