Stock manifold will be a choking point, you need the motor to breathe.
If you want stock manifold, get a fabricator to run twin gates off it.. grouping cylinders 1~3 together and 4~6 together.. the factory manifold surprisingly is "nearly" twin scroll, bar that little notch.
OR use a Havoc Fabrication modded manifold which merges each of the pulses into 1x gate. I would expect at least a 45mm or 50mm gate off it.
GTX3582 would be perfect, especially with that 3.0L pushing it along.. heck even a GTX3576 would be perfect.