1966 Dart 225 Slant/3 spd power/MPG?

Had a '69 Coronet wagon, 225, 1bbl holley 3.23 gears and the 833 o/d and got 22 highway.
With the 2bbl bbd carter I got over 25....
I have no clue what the '68 is getting 225, 904, 3.21
My '61 Valiant 225 1 bbl 904 323 got 15