There are some really tough things to work through but you can do it.
I have a 2004 swapped into a 99.
I'd look at: http://www.rs25.com/forums/f145/t125...oke-r-sti.html
The man that did the work is named Taylor and he did it right.
I just bought the car from him last month and I have to say it's a amazing swap.
The whole interior and everything was done including the carpet. He just had someone do custom work for the cloth in the door panels to match.
The other thing most people call out an issue with is making the dash mount up seamless against the door jam. If you need pictures of anything let me know. I can post them to www.subaru25b.com
I've got a few GC8 types I own now.