Before seeing the picture I thought they might have done a retitle. But thats definitly 41 thru early 47 styleing. With my 1938 1 1/2 ton they replaced the engine in 42 and retitled it as a 42. If the truck was used much there is a good possibility the engines not original. My grandfather had a small fleet about 10 trucks mostly stovebolts and it was common to have several engines in the crate around so they could be swapped quickly and the truck back making money if he did it that way it was proably common practice.
Good luck with your project.