It may fit with minor modifications (you may have to get a couple of the hangers re-located at a muffler shop). Another concern is that the exhaust may be too short and the tip of the muffler may not clear the bumper, which could cause some burn marks. I would contact Cobb to see how the WRX cat-back differs from the one they make specifically for the FXT. Or ask the question here and you'll find a few more people who are knowledgeable about the FXT...

 

Yeah, I hear cat-backs designed for WRXs (and STis for that matter) may come up on average 2" short of clearing the bumper properly. If your FXT is black like mine, it won't matter as burn marks won't really show.