from my experience with a 50 trim T3/T4 hybrid on SRT-4's this turbo is actually able to put down 500 WHP in a FWD setup, on a side note what are you doing about the hole for an external wastegate on the 5 bolt portion? if left open like that it will not boost at all.
If im just stupid and didnt notice what you said pertaining to that then forget what i just said lol but what i would of done is got a 5 bolt internal wastegate flange, brought a 3" downpipe out of it on the outlet side, and then brought a small pipe out for welding an external wastegate flange on it...like this example, which is the pipe furthest to the left, it is an O2 housing for a 5 bolt turbo that has an external wastegate flange welded to it...and it has already proven 690 WHP on an SRT-4 so i know it works