Hello welcome, just come across the thread sorry been busy,
If it's a uk car it will have a td03 as stock, Imports have to04's
Pop the bonnet and have a look do you have the coil pack off centre and a blow off valve attached to the tmic ?
Imports have shorter serial numbers too.
90% of impreza parts fit just need to make sure you get the right version that corresponds with your foz, exhausts are the same until the rear sections , the back box is longer, impreza ones do fit but will need to be altered, I think the standard injectors are grey, 380cc.?
As for ecu options you'll have to pull the carpet up and see what serial numbers it has on the front, some will require a completly new unit or a esl daughter board putting in, you may be lucky and be able to have yours re flashed,
Anyway get some more pics up and enjoy modding
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Sent from my SM-T210