Nice box, Art, the #10s are pretty elusive so congratulations on finding one! The contents look right to me too. The graphic rules on the back remind me of that single-fold insert that Master published and included in some other packaging, like the Century of Progress mesh bag. Have you seen that little pamphlet - do you have one?
And the box itself, even the rules graphic on the back, are pretty much the same as the large Heaton boxes - sorta like the #5, and I'd bet dollars to donuts they were produced by the same manufacturer.