Nice to see a example of the Cooper shoebox in use. I would guess the mounting tenon has a short rounded arm section to slip in to the 4 bolt fitter though. Did it have a NEMA tag by any chance?
*Update this got a new pole and fixture again last week! It got a new shoebox just like this one just like the other knockdown from a snowplow. It still does not work even though this is about the 5th time its been replaced in 8 years
I think this drop box is now obsolete in Brampton. I've seen FCO shoeboxes replace these cooper drop boxes on every occasion this year. I've seen refurb/NOS drop boxes used til' this year.