We have people ask us all the time "what supporting mods do I need to make (x) HP?"
Step 1 is to always address the basics, which is your valvetrain. There are multiple ways to go about it, as your pushrods can handle quite a bit of power... but if you already have the truck apart why not do it all at once? Regardless, by using this link, you can pick and choose the parts you prefer.
Our preference is to use the XDP (Manton) kit, but there are a ton of guys (us included) that have made well into the 4 digit realm using the basic hamilton kit.