Are you willing to stroke the engine or do you just want to keep it at 383 cubes.
Of the engine mods, and keeping it fairly stock looking, what parts are you OK with being changed out for aftermarket parts?

Getting to 400HP with 383 cubes to start isnt so hard as compared to a 318. A basic hot rod combo would be something like a;

750 carb
RPM I take
Mildly ported heads
At least a 9.0-1 compression ratio
Cam @ 230@.050
Headers into a 2-1/2 exhaust

Equipe the car with 3.90's/4.10's, a shift kit and stall converter to match the combo and you'll have a nice and decent basic hot rod combo. The above combo creates an easy 400 with a 360.

Stroking the 383 helps with a nice jump in torque. And that is what puts people in the seat.
IMO, I would honestly look for a good bit more power to keep people in there seat. It just add's to the awesome-ness of the experience. It will make for a memorable ride.