OK, got away without having to cut anything up, although that would've been a helluva lot easier! Took a 3/4" combo wrench and cut off the box end to a length of 2 1/2", then shaved the front and rear of it to a thickness of 3/16" and shaved the top and bottom to an overall diameter of 15/16". Then I slid the wrench into the slot and rotated it onto the nut. With a friend holding it in place, I unthreaded the bolt until the wrench wedged itself to a stop. Once out, I taped a nylock nut to the wrench, slid it back in place and threaded a new bolt through the mounting hole and into the nylock. 5 1/2 hour project, with 5 hours spent coming up with the modified wrench concept. After that, the old was out and the new in place in about half an hour!