I second the idea of leaving it alone. I have two daily user boxes that have some rusty areas and I like it just the way they are. I always say I'm not running a museum and if the items are perfect then I won't want to use them.
I would pull the drawers (and maybe the lower sliders and maybe the drawer lock bar), take care of the rust (and make sure the bottom's not rotted out, if it is repair), prime and repaint the repair, and be happy.
Just don't leave the rust to continue it's dirty work. Rust never sleeps...
Wow, now that you mention it, I too after searching the web have yet to see a 3 handle drawer. I wonder if that was a P/O modification or a Matco experiment.
Should be 33" wide x 18" deep. MB920 or 9200 for the bottom box, maybe.
The one lookin posted with square corners is more modern than the older rounded corners the OP posted. They made a 36" wide one, but I believe it had the full length drawer pulls, not the twin handles.
I've always likes the handles on those mac boxes.
I had one when I was working on the line in the body shops many many years ago. I don't remember what happened to it.