Who's tunes are you using now? The stock parts in these trucks are pretty beefy already... the stock bottom ends are good for a bit more power than you're even seeking, and the valvetrain about double what you're seeking.

You say reasonable effort on a rebuild... does it actually need rebuilding? Did something go wrong with it?

500hp build is very different from a 600hp build on these. 600 will cost quite a bit more than 500, even though the power is easy, the biggest thing there will be adding a built transmission to the list at 600. 500 it's not needed.

A clean, flat set of heads and some ARP head studs will be the first things to do. A fuel system of some sort will be a good idea. What are you using for gauges now? Anything?

Your parts list in your first post is a good start. We can help you narrow down a turbo and injector combo pretty easily, but you'll need some supporting mods. Mostly fuel system and some good gauges. A coolant filter would be a good idea to add if it doesn't have one yet. I'd also add an oil cooler rebuild kit to your list and an EGR delete kit if it doesn't have one yet too.

Moving this to the performance section...