Is this a good deal? Will it do what I want? Carb/Intake

Put a good tuneup on what you already have. Tweak the distributor and the carburetor and you should be in the 20 to 25 mpg range.
My dad and I were always tweaking the 318s for mileage. 21-22 was an average. Our 78 Volare with 318 automatic used to get 26 and 27 on the interstate. That's was with the original carburetor and distributor and a lock up transmission.
Super tune it.
That's milage on the Volare is impressive.
My folks got 21 mpg avg with our then brand new '69 Belvidere with 318 and torqueflite. NJ to Pensacola, with A/C on for some of it.
Only tweak was my folks had it set to use American High Test or Premium. In other words, the timing was slightly advanced and they used what would be the equivalent of 93 octane.