This brings a whole new meaning to the idea of split bus.
I think you're right, Scott. To my eye, I see a second 60A fused pullout that would have been a service disconnect. This was removed and replaced with the CB insert.
The double lugging of the lower service entrance (feeder?) conductor (at the remaining 60A pullout) intimates a history of lug failure from too much load.
Load calculation, load calculation, load calculation!
Is there a main or service disconnect ahead of this panel, or is it the service center? (What is the box at the upper left of the panel?)