like i said, an A/R .82 exhaust housing will work fine for top end flow (which was the discussion of this thread), but as mentioned, a decent exhaust wheel is required to flow that gas at the higher rpm.
fyi, the GT30 -11, has quite a small exhaust wheel, and is not suited to an RB30ET, let alone RB30DET.
plug in the numbers (3000cc, 7000rpm & 20psi) and you'll see that a GT30 (-14) core is recommended with an A/R .82 exhaust housing.
http://www.turbofast.com.au/TFmatch.html