Hey Andy,
Not a direct fit as the Foz is 3" longer than the Impreza plus the hangers are a little bit different.
If you get an Impreza one get someone to make up a flanged spaced piece for you to mount between the centre pipe and the Impreza backbox.
As for the hangers the backbox will sit very low so you can either bend the hangers with a bit of heat or get a set of short exhaust mounts.
Good luck and get it done - You know you want to be a hooligan, its well class when folk see the Foz and you can see them looking past you trying to see an Impreza.