Don't quote me on this, but I think this may have been one of the other models from the same period as the W60E's (and W70E's, W40E's, etc.), which would have been 1973-77. To help narrow it down, are your drivers front-loaded or rear-loaded (Is the back panel removable, or do you have to access the drivers /crossover through the front underneath the grill?). Also, are the front edges of the cabs curved/sculpted? I'm talking about the top and bottom edges that run horizontally across the diameter of the cab - On the W60D's, it has a curved/sculpted edge while on the W60E's it is straight (The front of the W60E cab is still beveled and routered, but the edges all run straight across the horizontal diameter, if that makes any sense). And does the rear of each cab say "Do Not Drill"?
Also, is this a 3-way design? I assume yours have the 12.5" woofers like my W60E's do, but do they have a 5" cone mid and a soft-dome-style tweeter, or does yours have a different makeup? Do they have the fried-egg tweeters instead?
All these questions should at least pinpoint the era the Super 60's were from. I've heard of them, but I've never seen a pair before.