Miles/gallon: Newer vs Older Cars

My 71 Sebring with a rebuilt stock 318/factory 2 bbl, 904 and 2.7ish:1 rear grears got 22mpg when moved from Seattle to San Fran down I5 keeping with the flow of traffic. The overdrive is the #1 improvement. Either run stupid 2 something gears, or get good acceleration and have an overdrive.
Aerodynamics have improved even if sometimes they don't look it.
Fuel injection is nice for varied conditions, but a well tuned carb and a warmed up car can do just as well.
EGR believe it or not helps economy.
The power they get from limited displacement is amazing as well, the simple non-turbo 2.0 Ford makes 160 hp in Ford's cheapest cars. A 6.4 would need to make 512 hp to equal that output per liter. The SRT only makes 485, the old 426 even less. That 2.0 is direct injected which is really a big step forward. Then they can eliminate the throttle body restriction as well and control it more like a diesel.