Oh, those pesky wheels!
Well, tool boxes were a personal kind of thing anyway. Either way would be justifiable. So, disregard my last and leave it as you have it.
I was working from memory of the one in the museum. My reference pix are divided: about half have no toolbox at all in the rear, some have them on the other side, most have the hasps and locks to the interior with the hinges nearer the wheels, some have them mounted the way you have yours, and at least one even has the hasps/locks on the front end.