Unless your present muffler is really bad, a new one won't help. I got one a
few months ago from Bus Depot and it actually made the sound louder than
before. Not a complaint, though, as I like the resonance of it.  There's
something appropriate about hearing the engine in these old cars, in my
opinion, but to each his own. I find that the rear mattress deadens the
sound a lot in itself--do you have a mattress in there?