Well the 71 383,s came with a holley (a shorter single inlet style) so a stock air cleaner should fit them.
If it is stock a 625cfm carter or 600cfm EDDY should suffice but add headers, good dual ex and even a mild cam then a 750 EDDY should be better. 60 miles to half a tank seems thirsty but what gears and tranny do you have? mostly city or hiway miles?
myself I have forgot what I get to a tank
just keep an eye on the guage.lol. I,m running a 800cfm EDDY on my warmed over 383 because I know I will be going to a stroker 383 in a couple of years and didnt want to buy a diff carb just a few years later.