Small block mileage

I've gotten 23 mpg with my 74 dart 318 2 bel. No special tuning. It's mostly about how you accelerate from a stop to get up to speed...and hwy or street.
I drove it routinely to venice beach from fresno and 23 was the mpg.
I've gotten 18 from my 1500 when I had crappy rock hard discount brand truck tires..and the Taylor spacer driving 72 mph on the hwy...but those factory computers actually retard timing under load/acceleration...so you have to stay out of it. They got to 20 from 36-40.
Stick a 500 eddy 4 brl on a stock 360 and that helps quite a bit over any 2 brl.

Slants get only a hair better than a teen, like a few maybe

Your results may vary.