That's a huge turbo. All you need now is headwork, aftermarket FFIM, huge lift cams, 1600cc injectors, three walbros, standalone, TH400, 315mm wide rear drag radials, C16, and a proper tune.
See how much power that stock block can take!
I say go with a 4 inch exhaust all the way and just run open downpipe!
What exhaust manifold are you going to use? So far, either custom or the MTR one (maybe) are the only ones that will support that turbo you've got there that I know of.
You put that GT45 on a chinaman manifold or any other without reinforcements, and you will fail, bigtime.
Seriously... Try a 61mm turbo.