In the 80s I owned 2 challengers where we took good running 375hp 440 magnums and did rings, bearings, gaskets and oil pump. (These engines were around in good condition then) Heads were left alone if they looked fine (usually 906) but added the old stand byes- Torker intake, Holley 750 carb, blackjack headers, cam- I ran the mopar 484 purpeshaft, shift improver kit and a sure grip rearend. With a 3:23 gear the one ran high 13s. Even with OEM heads it asy to make a 440 run provided the compression is there. Years ago a mopar mag built a 440 to stock 375 hp specs. THEIR dyno pulled around 360 hp. Then they added an M1 single plane, Holley mechanical secondary carb, 509 cam and headers. They then pulled 425 hp. Heads were restored 906s but not bowl ported or dressed. 509 cam has lots of duration but the point is how well the motor responded.