RE: 424 racing in SW MO
Replace that bolt with a 6/32 threaded rod. Drill the front of the muffler for the rod and run a 6/32 tap through the back of the muffler. put a lock nut (nylon insert) on the front and install the rod. Tighten the back down and put a lock nut on the back. No more problems or a lost back half of the muffler.
Denis