[Critter]

Are you talking 400 hp at the crank or at the tires? If you are talking about crank hp then a cam and good tune can accomplish that (usually). No need to change any of the other stuff. If you are talking wheel hp then more will need to be done.

One thing to note, you can't just bolt and LS1 intake down to a truck LSx motor without swapping other parts also. The front accessories have to match the intake. In other words if you put an LS1 intake on a 5.3 the throttle body will be pointed right at your idler pulley/belt.