Here’s is a Chrysler Engineering dyno test from January 1968 on a GTX/RT 440 4 bbl, ran with full exhaust, air cleaner, vacuum advance, heated intake with riser open, using the production high performance camshaft, AVS carb.
I think some of the confusion on horsepower produced is due to SAE standards back in the day. One rating is with accessories and exhaust, one without.