Not Hdwrench but IMO a pipe change would get you there, even Bassani power curve headpipes with your slip-ons would be an improvement if you just have to stay with the dual look. A FatCat would be even better. No mention of carb or EFI. Tuning especially individual cylinders with cross-over duals is not essential but helps the driveability and hp/tq. Got a good tuner? What tuning device / hardware are you using?
BTW the closer lobe centers and short duration of the TW6 IMO would yield more low end TQ. I would not expect any more power. Better street feel, after all we don't ride the dyno.