Ok but here is another problem Howardtm. Your wanting power with mileage. That is like asking the bank for all its money but not robbing it. Any time you port/polish, or want to have extra power your going to have to give something in return usually mileage.
I think a different turbo, injectors, fuel system upgrades may acheive what your looking for better then porting your heads.
An engine that has high mileage usually is going to have low mpg. It maybe time for a rebuild. Just a mild rebuild may increase your mpg's. As a fresh engine will run more efficiently.