Streetmaster to Airgap

Seems this article is the rest of the story:
1970 340 High Performance Mill Dyno - Mopar Muscle Magazine

They went with additional changes including headers, valve springs, etc. Final pull was 392 hp (first pull was a near stock build at 291 hp).

Also, in what crazy *** world is 15 hp NOT a notable improvement? Plenty of folks spend big money on parts like heads to get that much gain. A 22hp difference at peak is also nothing to sneeze at. But take a look at the results from the article above, and it just goes to show that it takes the right COMBO to get big gains. Add more cam, headers, and a bigger carb and the engine went from good to great.