Anyway, I'd be tempted to convert your rear bracket to "soft" point, just by

making it a clearance fit. Or you could say "bull", and just inspect the
weld adjacent and the attach surfaces every X hours.

Al;

If the manifold muffler were decoupled from the engine, then the rear
bracket would also need to be de-coupled.  I've chosen to have the entire
system rigidly mounted to the engine.  Floating the rear bracket would cause
something to break.  

I don't think there is going to be any visible "sine wave" in the short
length of 2 3/4" pipe.

Al G