Aha - found another Chicago tool (a spanner wrench) along with another defunct American company tool - Covers Company, out of Bedford, Ohio. (Have since found out that Covers Company is even rarer and more obscure than Chicago Spec.). That 4-way wrench is really nice.
The Cover wrench is the top one. Notice how it has a sink drain wrench built into the side - I included a pic of the Chicago wrench on top lining up the corresponding detent's.
Wrench openings on the Covers are 1 7/8", 2 1/8", and 2 9/16". The dual opening on the Chicago wrench is 2 and 2 1/8. You plumbers out there can tell me if those sizes are typical - I have no clue if they're old sizes or still used.