383 build for efficiency

for best mileage you need hi compression.
reasonably hi lift cam with short duration...and must match your drivetrain
as well as your engine.
..your maximum lo speed torque must be your cruise rpm,many have installed
an od transmission and had their mileage go down because they were cruising
at an inefficient rpm for their motor.
an o2 sensor and wideband a/f computer can really pay off here
correct gears,small primary venturi,light weight,lock up or lo stall converter.
very complicated subject!