Ron,

Don't know if will work for this application, but I finally hit on a fail proof muffler extension for my 46 engines. I bought brass tubing at the LHS that will slip over the end of the muffler and cut the appropriate length. With the Dremel, I cut 4 slots parallel with the tube from the end to about 1/2 inch back. I then used the smallest hose clamp I could find (the kind you tighten with a screw). You can even put a little bend in the tubing if you want.