Exhaust manifold, turbo, appropriate intercooler for the power level, and a set of bigger injectors (the standard reds are almost maxed at your current level)
Interally to the engine you need NOTHING at all, they are fine for 400 in standard form, alhough the 2.3 rods dont like a lot of rpm so the 2.0 engine would have been a better bet strength wise ultimately.