Ok, the car is registered as a gtst so it dosent matter if you take the turbo off or not, if ur restricted to a non turbo u can't have a factory turbo registered car, regardless of weather u have the turbo attached or not (yes it's dumb)
Plus as turbo motors run a lower compression ratio (google this) then a non turbo motor they will make alot less power when compared to a factory rb25de (compared to a de turboed rb25det)
.... Unfortunately Natro motors require hi comp to make power and as uve essentially got a low comp rb using a Natro induction method your going to make sfa power (which is fine if your not interested in power) but as a heads up your going be down at least 20rwkw compared to a factory non turbo 25... Which only make about 100rwkw to star with so.... Yeah