I believe you will achieve 400hp easy for 450 you will need the intake manifold my friend.
BHP = Air + Fuel
(sry couldn't resist)
Big Turbo need Large Port in their life unfortunately but that doesn't mean that you can't install a little later. Since you are building it correctly from the beginning you are going to have the most of it.
If you don't have enough money for IE, SEM, 007 or similar large intakes then i would suggest find a used one from ebay from and AEB, AGU, AFYC which come with Large ports from factory.
The differences are :
Small Port Head Engine Codes :
ADR, AMB, AMU, APT, APU, ARG, ATC, ATW, AWM, AWW, AWP, BEA
Large Port Head Engine Codes :
AEB, AGU, AFYC
Small Port: 43.2mm X 23.2mm
Large Port: 55.1mm X 26.2mm
They are a little bigger and you will have a little better flow they are not as good as the much more expensive ones(like Integrated, SEM, 032 Motorsport) but it will be better with a small cost.