sorry i am not driving silvia but i saw this thread i just give my comments.
350 whp is not that much to do. (i mean in the save save side)
1) turbine u can buy garrett gt2876r (ballbearing) this can keep your ori manifold
2) injector 800cc this can allow u go further in the future.
3) u want power fc.....??? for me for the save side go for e-manage
4) japanese can easily hold 350 whp (no problem)
5) still got money go for high cam brian crower 280 is cheap
6) beyond 450whp need to do more on the engine already.
by the way i am azracing tuner. hope this can save your pocket money anything u may pm me.