Pretty simple to get 400 HP out of your 440, should be no need for a crate engine. If the engine is fresh just put a good dual plane aluminum intake under your 770 carb, install some headers and good free flowing dual exhaust, good ignition system and you should be pretty close to 400 with maybe a little extra, good luck.
1968 Plymouth GTX 1974 Dodge P/U Long Bed Stepside 318 2019 Ram 2500 6.4, auto, 4WD