Small block gas mileage DD magnum/LA ?

That’s the way to do it! Nice job.
What dual plane from Edelbrock?
Can I assume a Hyd. roller cam was used?
How big was the exhaust pipes and how was it run and with what mufflers?

The intake is a 318/360 performer.
Obviously it could do better with a larger runner intake since the ports in the heads are about 1/4 bigger all the way around.
(At least the air/fuel charge isn’t hitting 1/4 inch walls if it were the intake that was larger)
Yes, a hydro roller with OE lifters and 1.6 rockers with Hughes Engines springs, retainers and locks.
1.92 intake valves and 64cc closed chamber heads.
Dual 2.5 inch out of 3 inch collectors and flowmaster 40’s.
The 2.5 inch pipes literally cross through each other and then out in front of the rear tires.
How it was run?
For checking fuel mileages I ran it on I40 at 80-90mph for 700 miles.
Averaged 2,500-2,600rpm.