Go look at a GTir IM. There is a whole lot going on apart from just cut and shut
GTI-R Flange/lower runner with ITB
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SR20VE Lower runners
A few things
1) Port/lower runner spacing seems to be different
2) Runner shape
3) P11 VE is reverse taper. P12 is straight (shouldn't have an impact, just a FYI)
4) Vacuum ports on the lower manifold which need to be tied into the head flange for it all to work
5) Lowport vs High Port (if my memory serves me correctly)
And that's just to name a few. I have seen a few folks try and just give up. It actually looks pretty close on first glance however. Easier (and probably cheaper) to just buy a Xcessive, a set of horns and weld her up.
Not trying to disuade you, but its a little more intricate than just cut and shut (and there is proabably good reason not alot of folks have went that way)
Also, tuning speed density or TPS with ITBs is a bitch. There are tuners capable of doing it as this is nowhere close to a foreign concept, but you have to find the right person.