318 Magnum 70 Dart Gas mileage

I recently purchased a 1970 dodge dart with a 318 magnum out of a 98 durango and 727 auto trans Its been converted to a 4bbl Edelbrock carb with long pipe headers dual 2 1/2" exhaust with flowmaster mufflers. 4:10 gears with posi trac. 14" Wheels. Wondering what mods i need to do to the car to get decent gas mileage so i can afford to actually drive her around. This is my first classic car so alot of this is new to me.

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