Tuning a DD 383 for optimum mileage / 1/4 mile performance

My advice, get a spreadbore design carb, QJ, or TQ, or even a Holley spreadbore.

What do you have for gearing? That is probably a large factor for your mileage and of course will "adversely" affect strip times, as you are likely running low

I realize "different era" here are two examples

Before my old 440-6 RR scattered all over I-5 up near Stockton LOL with a stock cam it would get 13.8 mpg, 3.54, 4 speed, headers. This was with an 800 Holley

Later on I swapped a bone stock low miles 340 into the car. With headers and "some sort" of spreadbore, it would get over 17 mpg at 70 mph. Same 3.54 gear, it ran right at 3K RPM at 70

I was an am "not" a careful driver

Also I don't know your budget constraints CONSIDER EFI. Even TBI (Holley or FItech) can be calibrated better than carb.

GET A WIDEBAND O2 if you don't have