racers plz help my set up

well in the winter im gonna change my rear end gearing and tire size..just wanted a few pointers and opinions...
i have a 71 valiant eddy headed 408 power from 2500 to 6200 i have 3.91 gears and 26 inch tall tires...i want to go faster with out tearing apart my motor....i dont take it on the street ever...any body who has ant 2 cents plz let me have it....thanks fabo peeps