Getting power out of a 63 /6?

Welcome to FABO! More power=less mileage for the most part. It's hard to get both but not impossible. Gearing is about the only way to dramatically do it. An overdrive trans with a low ratio rear is the best way. That way you have power on take off but reasonable RPM on the freeway. Cam and carb improvements can help also but are limited in what they can do for both desires. A low restriction exhaust can help also if it's done right.