I was looking at my body brackets and noticed an oddball. In the photo, it's on the right. It is slightly wider than normal and it has that oval shaped slot for the body bolt. Is it for a Model T or something else?
Typically the 26-27 brackets were slotted,with clipped corners. Don't know about your round corners.
Are you sure it didn't just wear that way?
I have some, they came off old wood truck cabs,never seen any on any year car,i have done about 300+ in my time.charley