Well its known that you can put an 04 bumper on an 02 so I would assume you could do the opposite. I think you might have to buy a few clips or something but nothing crazy. Also you have your taillights. They would work on the 02 bumper but you would need to dremel the little cutout for the round part of your taillights. Or you could just get 02 taillights aswell.
I'm guessing hood, bumper, fenders, radiator support. There are a few threads on nasioc about people doing stuff like this. I recently saw a guy rebuild a salvaged 02 wrx with an 06 front end. it was sweet!