The 261 is like any other engine, more gas better exhaust. Bolting on a dual carb manifold is likely to help but keep in mind that the 261 was advertised to make under 150 horsepower in stock form. The 54 version made 123. So in order to increase horse power without major rebuilding means bolt on power enhancements. So you are stuck with intake with dual carbs, dual exhaust, maybe even Barker High Lift rockers (pretty rare to find these days). Otherwise you are left with optimizing your current set up. One thing is that a 261 used a different carb then the 235 but because they looked virtually identical, its not uncommon to have a 235 carb on the 261. You might want to sort that out as the proper carb will help. Also optimizing your timing, making sure the vacuum advance is working. Does your 261 have a governor on it limiting the rpms.
