59 inches wheel mount to wheel mount I suppose. I spec'd a 61 inch wheel to wheel for my 1940. That allows for wider tires that are offset to the inside by 1 inch.
Do your own measuring, and don't take my word as "law". A 1940 should have a box that is 48.5 inches wide. It also has about 11 inches of fender on each side. Using rims that are 7 inches wide, with 4 inches of backspacing should center you up pretty well in the wheel well. A maximum tire size would be about 10 inches wide...lets say a 255 series tire. Can't garrentee that you won't have any rub anywhere, so like I said take your own measurements and do your own math. I don't have my rear in the truck or the tires, or the box to see if it all does fit.
John
