Doubt you'll increase your gas mileage with dual carbs, but if you still want to do that, use an Offy dual single barrell intake manifold and a set of Fenton headers. Both are repopped if you can't find originals. You could use Rochester carbs, but Carters are better. Mufflers depend on how loud or mellow you want the noise. Cruising speed has a lot more to do with your gearing, not the engine.
