2.2 what? liters/ quarts/ pints/ cc/ gallons/ tons/ pounds?
LOTS of low deck Mopars (then 383s) delivered decent mileage "back in the day." The only reason the 400's were poor in their day is that they were built in the midst of the '70's smog junk, were low compression and aweful cam timing.
Pull that big cam put in a "stock" cam and take a look at the timing curve. Depending on how the carb is jetted AND THE REAR RATIO AND TIRE SIZE there's no reason in "Murican" thinking those girls should get at least 14 MILES per GALLON whatever that transfers to in your end
"Real life" old world example: Back in the day a bone stock 69 Roadrunner 383 4 speed would have come with 3.23 rear gear. You could expect 15MPG or better out of those and they were considered a performance engine. Those WERE high compression
