I've never heard this before?Chrysler says they only made 280hp. Chrysler admits to over rating the 383's. see if you can find the October 1967 hot rod magazine article where Chrysler gives edelbrock a 383 to dyno test. look at the mopar engine manuals for real net horsepower. everything falls back to 280hp.
This article shows differently, and a 67 383 is different from a 69.
https://www.hotrod.com/articles/mopp-0209-383-engine-restore/
Note that with headers, big carb and an aftermarket intake over 400 HP and 433 ft*lbs of torque with a stock cam.
But they did use hypereutectic pistons, which is what I have in mine.