I should make it clear that my tangential muffler uses a slotted tube that runs down through the length of the 5" tube.  This tube is also inconel and is welded to both ends, thereby adding strength to the flat ends.  I utilized Lynn's coupling design to allow for movement between the muffler and the engine.  

Mark;

This is interesting.  Would you care to give a bit more info – or perhaps provide a sketch? Where is the exit from the muffler? Does the exhaust exit through the slotted tube? How big is the tube?

Al