How to get 400 hp out of 1971 340 .30 over

I’ve heard a lot of small block guys say their car “should make 400 hp”. I think some folks need to recalibrate their denim dyno.

FYI OP, I have a similar build to yours but in a 360. Flat tops, RPM Intake, cam, and 750 DP. I made 413 hp / 430 ft lbs.

Compression ratio and cam specs please!!!!

TIA