OK, Frank, I bow to your superior knowledge of all things that vibrate.  I
also see how the muffler being bolted directly to the engine could transfer
some harmonics.  Here's my big question of the day:

How much movement do these muffler mounts need to do the job?

The Tiico mounts are as soft as bubble gum. Recently, my exhaust was not
welded together, and I bounced the muffler around freely.  You can put your
foot on the muffler and bounce it up and down a few inches.  That is
excessive travel to me.  When the whole exhaust system is bolted/welded up,
the rigidity of the system reduces the distance the muffler will bounce.
What that tells me is that the weight of the muffler is being held up by the
rest of the exhaust system, not by the mounts.

I can see where a small amount of vibrational movement would be beneficial,
but these mounts, I think, go beyond that.  Maybe a rubber washer or grommet
would do.  What do you think, Frank?
(And do you still have the counterweight on your header?)

Bill Marshall
85 GL Tiico "Pandora's Box"
Bradenton FL