You want a '96 and up. This gets you the 2.2 unless it's a Brighton. The earlier cars and Brightons are 1.8's and are dogs. You'll enjoy driving the 2.2 until you do your upgrades.
In '97 the Imprezas got the new nose with the different hood/grille/headlamp profile. An RS hood is a bolt-on for these. With a '96 and earlier car you need to change the lamps and grille for it all to work.
The ass-end of the car is the same, regardless of year.
If you want a lightweight car for a donor find one without sunroof or power windows. Makes a big difference.
You can see my 2.2RS project here: