360 driver build
I like TQ's. A spreadbore carb is IMO an excellent choice for a stock to dual purpose engine/car set up. But, in truth, any carb well tuned will deliever mileage and power. What is under the carb will have a big effect on mileage 100 times more than style/maker of carb on top. Even if out of tune and miss adjusted.
(I'd look into tti's before Dougs. )
As far as a mileage getter is concerned, a helping hand in this search and in a big way would be a overdrive tranny. Let me give you some mathmatical numbers as how the overdrive works out.
Gear ratio X's overdrive ratio equals new final drive ratio or, with numbers;
4.56 X .69 = 3.1464 or 3.15
4.30 X .69 = 2.967 or 2.97
4.10 X .69 = 2.829 or 2.93
3.91 X .69 = 2.691 ...a bit low in final drive. Though MoPar did offer a 2.45 axle ratio at one time.
With the final drive ratio's as seen above, figure your cam specs and useage to those ratios since your after mileage. You can still use a low duration cam. The smaller cam will produce mad torque that will be whipped out by the low gear set. You'll have great get up and go. But instead of running out of steam early, the OD steps up to bat taking over for the Hwy. duties and conserving gas.
Now, your armed with "Food for thought!" and the probabl need for wider tires to hook up.