I am also amazed... my slightly warmed-over '70 Valiant (stock 383 rebuild, .484 purple shaft, 750 vac sec, dual-plane, A833, 3.23 rear) got about 15 mpg on the highway at 65 mph, around 12 mpg mixed city/hwy and my lowest tank was 8.3 mpg since it was all going to the store for a quart of milk 1/4 mile away
drive

And my '76 Valiant with stock /6 and OD A-833 (don't know the rear) would get about 23-24 mpg at a steady highway cruise.

Maybe they're talking Imperial gallons? work