The square hole and the clamp that goes all the way around the hoses and pops into the square hole is correct, and was used from beginning of production on 1964 Chevelles all the way through the end of production on 1967 Chevelles. So the piece that your pic shows is something that someone made and put on the car, presumably because they broke or didn't have the original clamp. I can't explain why your inner fender has no square hole, other than to speculate that if you sanded the paint off you would find that the square hole was filled or welded shut at some point, probably at the same time as the repairs around the battery tray that you mentioned.