I would advise you to first find out what the emissions implications are in your area of Texas. Does your truck have to be run thru emissions every year or are you in an exempt county? IF you have to pass emissions, your choices are considerably fewer.

Your current engine is a Vortec that has a specific manifold with the injector spider. The manifold fits Vortec heads with the eight bolt intake pattern so you cannot just bolt your injection/manifold assembly to an earlier set of heads. Your injection system is not tailored for a 400hp engine and never will be.... Be aware that this engine is 96 thru 99 (and a few 2000 models) but is not a throttle body engine that was 95 and earlier.

Your easiest route to a feel-good performance is to find a 96-99 350 Vortec engine and bolt it in.....literally a weekend project. The engines are really common and cheap. They are roller cam engines and you can slide a little hotter cam in before the install....no too hot though.

The stocker 350 Vortec engines listed something like 330 hp. There are two basic models, one has EGR and the other does not. The non-EGR models came in larger trucks....if you have emissions to pass, dont get the non-EGR one.

The result will be an engine that looks completely stock but will have more pickup for your pickup. Cheap to do too.

mike in tucson