RE: silent beauty muffler mounting bracket problems
Unfortunately, you probably DO. I have purchased, and actually had success, with a product called "alumaweld" brazing rods. Took some practice to learn how to make it truly flow and bond, but after I got it worked out, I was able to braze on an aluminum washer to the thin metal, then drill and tap that whole thing. Much better.
The other thing is to be absolutely certain that the muffler is bolted into final position on the engine, and then the bracket is mounted in such a way as there is NO torsional or tensile stresses on the bracket. THAT will solve the stressing of the attachment point. One other issue is to be sure the strap/attachment itself is of rigid enough material so that it is NOT flexing under dynamic twisting force from the engine. The idea is to make the box, strap, muffler, and engine a single "unit" of mass that moves as a "single unit". Stuff won't break when those considerations are made.
The whole strapping mufflers and headers and canisters issue is more art than science, and I think more frequently "luck" than "skill", honestly.
Don't give up on it! I'd get some of that aluminum rod stuff and learn something new!! It can be fun to learn your own fixes for stuff, if you're inclined.