Added Ford wheel info.
The '67-96 Ford F100 wheels will also fit your '40 pickup, they will be wider, maybe as wide as 15 x 6.5", 5 0n 5.5 lug pattern. The big difference will be the hub cap knobs, which will be external. many of the later model Ford wheels will be F150's in lieu of F100.
The F100 wheels are generally rated for 1,500 lb's where-as the F150's will be !,800/2,000 lb rated.
I learned at a very young age the importance of having the correct wheels on pickup trucks.. My father was a Ceramic Tile & Marble Contractor, his trucks carried a lot of weight to and from jobs. From 1940 on my dad would not buy a pickup that did not have the heavy duty Artillery type wheels with 6 ply tires.
I was with my father in 1940 when he bought a new 40 Chevy 1/2 ton, dark blue with black fenders. I can clearly recall dad telling the salesman that the truck had to have the HD wheels with 6 ply tires.
The common half ton wheels would crack and split at the bead line with 6 ply tires, which caused a real mess to the rear fenders.
By the late 1940's the manufactures phased out Artillery wheels in favor of the split type wheels that were common on 1/2-3/4 ton pickups through the late 1970's.