Slant 6 Split exhaust

Anybody have any luck putting split exhaust on a slant 6? I converted the one barrel to a two barrel Super Six setup, and noticed a difference. I'm now thinking of adding split exhaust. Any thoughts? The say you can gain 15 hp., but that seems like a stretch.

Can just put the larger 2" or 2.25" single exhaust all the way to the back. That will help lots.

Factory exhaust pipe is super small.