400 hp is fairly easy to do if you're willing to buy a set of Edelbrock RPM heads and some semi-custom pistons. What you want is something close to 10:1 compression with zero deck, a 0.036 head gasket and the closed chamber heads. Use a Performer RPM intake manifold, a 750 carb and a mild cam and you'll be there. The Mopar .528 solid is probably too big for a street driven 383 but it depends on how heavy the car is and if it is a 4 speed or auto.

You can do the 440 crank trick but it costs more and makes 500 hp which is 100 more than you're looking for.