Small block gas mileage DD magnum/LA ?

Maybe it’s the gasoline around here but I find that my 5.9 just simply likes the 89 octane and hates the 87. The curve on the distributor is hot rod like. Not to quick. For me, it is what it is. But when I go out of state, it is fine on 87.

I do favor the LA for intake choices and the verity of available parts. Ether way you go, 20+ mpg’s should be obtained. My roadways are generally flat. Not like the desert states, but pretty good. Long Island is wedge shaped high in the north to beach sands in the south, wavy east to west.

If I was doing this, (318-LA) it would be a simple cast iron OE intake, or the right aluminum one w/OE heads with the use of a small primary (electric choke if possible) TQ and dual exhaust H piped. A mileage cam and a maximum compression of 9.0-1 with a high energy ignition.