One approach is to use a BIG muffler with a quiet tone for good exhaust flow without all the noise. I like to use mid-1970's Cadillac mufflers. They are made with 2 1/2" pipes in and out, and one of them is rated to flow enough volume for a 500 cubic inch engine. Dual exhausts on a stovebolt engine with those mufflers would flow like big straight pipes, and be extra-quiet.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!