The rams' horns for the 300 HP 327 used 2 1/2" exhaust pipes. Combine them with mid-70's Cadillac mufflers that have front and rear pipes that are also 2 1/2" each. Each muffler is designed to flow the output of an engine up to 500 cubic inches. Two of them make a 350 breathe about like it's got straight pipes. Put a crossover pipe ahead of the mufflers to improve the flow even more.
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!