RE: Securing the Muffler
Through drilling is not an option on the Tower muffler. The header extension and its length is a contributing facrtor as well as exactly how it is designed.
As one of the gentlemen already noted if you are using any kind of gasket on the two mating surfaces then you need to loose those, not needed and they definaately can contribute to loosening especially when two separate gasketed surfaces are involved.
John