Small block gas mileage DD magnum/LA ?

5.9 Magnum, EQ heads with LA intake bolt pattern, Edelbrock dual plane, Edelbrock 1406, HEI with a .050 gap, NGK plugs, 1-5/8 long tubes, 214/224 Oregon cam, 42RH, 3.55 rear gears, synthetic lubes in engine and diff.
24-25 mpg on the hiway in OD and lockup at 75 mph.

18 initial, 34 total and 50 or so with vac advance.
Averaging 14.5 AFR.
Then I put a Holley 770 on and never checked the mpg after the change.
There you have it. A recipe we can all follow. Thanks