I was unable to locate any with that location, but if you've found others with that attachment, it must have been a period Altec placement. As I've said, I'm hardly an Altec specialist by any means, but every day somebody posts something that is new to many of us. Your's is another to filed away in the ever-decaying memory banks!
In the end, though, you have a set of heritage Altec speakers that somebody originally paid a hefty chunk of money for. Looking forward to watching you bring them back to their former glory!
GeeDeeEmm