318 MAX fuel economy builds?

Back in 1976 my dad bought a new Volare. He was always tweaking on the carburetor and the timing to get better fuel mileage. He was making trips from Illinois to California and Massachusetts. I think when he was finally done with his tweaking he was getting 26 to 28 miles to the gallon with that car. It had the lock up transmission and I think a 2.76 rear gear. But I could be wrong on the gear.