Dual exhausts make the engine sound better, sort of like the split manifold on an Austin-Healey 3000 or a Jag XKE. For an actual performance gain, "There's no replacement for displacement"- - - -find a 250 engine to replace the 230, or relocate one motor mount and install a 292.
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!