Converting a stock manifold to a split system and retaining the original heat riser is by far the most effective way to get dual exhausts that work- - - -sort of. It doesn't really improve performance, unless rattling windows a block away with harmonics is considered to be an "improvement"- - - - -but you'll create fewer problems that way. The trick is finding an old geezer welder who is good at welding cast iron. They're pretty scarce these days!
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!