318 simple bolt on setup for more horsepower

My '65 Ply with 318/2.94's got 20 mpg. We got 24 mpg with a Aspen R/T that had a 318 3-speed OD.
It's an 833- a true 4 speed, just 3rd gear is an overdrive. But yeah, I got around that with mine with a 904.

I call bullshit....
That's essentially built to 340 specs. Only thing lacking is the bore. And I get the same MPG on the road with a 340 with 3.2s so I don't see how that's far fetched at all.