From the length, almost certainly a carpenter's toolbox. The length is necessary to accommodate handsaws. They generally came with a tray in the top, slightly narrower than the width so that you could put your framing square in the box, with some of the short leg sticking out a knockout in the top*. The top should have a clip or two or some wooden brackets, or the rivets indicating that they were at one time present; the saws (one crosscut, one rip) went on the lid. Google "craftsman carpenters tool box," and see if the images match what you've got.
The end handle would probably have been for hauling it out of the truck and maybe helping to balance it on your shoulder while carrying; a carpenter's kit would be light enough that a shoulder carry would work (unlike a mechanic's toolkit, which would tend to crush your shoulder bones).
Interestingly, they're still made, by more than one company (including Proto), so they still serve a need; somewhere, there must be carpenters who carry handsaws...although the new ones I found didn't have the saw clips, so maybe they're just for long tools.
I own one (Craftsman also, as I recollect), purchased because I used to drool over them in the Big Book when I was younger; but my carpentry is 99% on our half acre, so I don't really need a portable box.
*I've never tested how that works. I suppose you slide the leg through the slot while the lid's open and the top tray's out, pivot the square down, put the tray in...I think I'd just carry the square in my other hand.
