318 MAX fuel economy builds?

Along time ago, I pulled a 318 out of a 67 belvedere, it had a factory single plane and a 2 barrel Stromberg carb. I shoved it in my 72 Demon complete with 727 Trans. Rear was 8 34 with 2.94 gears. Engine was real loose worn. Tuned it as best as I could, points you know.Decided to move to NJ from FL so ripped out the back seat to have room for all my tools. Stuffed entire car with tools and stuff .til I could barely fit inside. Estimate 1000 lbs easy. Started on trip, thought the fuel sender might have given up the ghost cause it wasn't moving. Pulled in for. Fuel and was shocked. I was averaging 24 mpg. Of course is was only going about 60 to 65 and with the sea level air and cool night time Temps probably contributed to the mpgs. But still thought that was pretty darn good. Of course it was 1987 so better fuel quality? Alway got in the twenty plus mpgs and I had a heavy foot in those days.