What kind of gauges are you installing? Should be compatible as far as wiring and vacuum lines ( for boost gauges ). Wiring is usually universal for most gauges and the only difference is the reading of the units. metric vs. standard. Im a noob at doing this and its pretty easy so it should be the same for you. Good luck
If I remember right, Nabisco had an install on on a cluster install. Or was it scoobymods? Maybe it was a thread on Nabisco that went to scoobymods... oh well . They did a detailed thing on putting on the JDM impreza gauge cluster to an american Rex. Don't know much else as I didn't read further.
i just read that you have an 05, so that installation guide would NOT apply to you, but i dont have enough knowledge about the 05's yet to tell you anything differently
as far as i know, USDM and JDM STi gauges should be swappable directly. if you want JDM sti gauges on your sti, unplug the neg on the battery, take off the trim around the cluster, unscrew the cluster off the dash, remove harnesses, take out USDM, put in JDM plug in all wires, screw to dash and put trim back on, reinstall neg on battery and enjoy