Smallblock efficiency or How to have your cake and eat it too

When I had my '73 Duster 340/4 speed ('71 clone) I ran:
-Mopar replacement electronic dist from NAPA
-ThermoQuad 750
-GM HEI module conversion eliminating mopar ECM & ballast
-NGK plugs gapped to about .40-.42....initial timing at about 16 BTDC w vacuum advance.

I tested the fuel mileage a few times, under "normal muscle car" driving conditions = basic highway speed, with once or twice hammering it, opening the 4 BBL to pass with authority LOL
I would always get 26-28 MPG and thought that to be pretty good, considering an average new vehicle with all the sensor BS and EFI would struggle to get that!