If you already have a good running LS2, just go to the dealership and order an L76 intake and L92 heads right off the shelf, add a cam and you'll be around 550 hp and they aren't high dollar performance parts, just o.e. parts off a truck and a Holden.

Although, I do totally agree with MuscleRodz' answer 100%, if you absolutely have to have more hp, that's the best way to go.