Poor Gas Mileage

I just got my 71 Sacmp 225/6 back on the road. I am only getting 13 miles per gallon (between St and highway use). I have added new points ,condensor, cap,rotor, carb, plugs, exhaust manifold, and more.What can I do to increase mileage? The engine idles smoothly at low rpm`s and the car eases into gear. How many MPG`s should I be getting?