I'll bet that the same company made the boxes for both MAC and MATCO back in that era. The only difference I see is the drawer handles being different styles between the brands. On my MATCO Linemaster setup from 1979, each box has the model number and date stamped into the metal backside panel on the lower left hand end, as you are looking at the rear of it.
It was stamped into the metal and then they painted the boxes. So there is not much obvious contrast, and it is kinda easy to not notice that it is even there.
Perhaps give that area another look ?