Amuse3d just get a 04-05 XT and you don't have to do the STi swap. It comes with the 2.5L STi motor, but smaller WRX Turbo and WRX TMIC. Engine wise you just have to upgrade the Turbo , Down pipe & Intercooler and your set.
Hard part is finding it 5MT in good condition. But there have been alot of happy 4EAT on the forums.
By the way the STi hood scoop is from the '03 Bug Eye. Stock is about a inch shorter.