Rally Performance was the vendor selling the swap kit. They said it wa almost all bolt on, but would take quite a bit of time to do.
Here is an idea, just an idea. Are you getting the same color STI as your WRX? Buy the STI, swap everything over, and then sell the WRX afterwards with the new 2004 front end.
Couple things you may run into problems with. Your morrettes are not HID, the STI lamps are, may lead to a lot of wiring. I am not sure of the requirements of the two, but am sure they are different.
Also, no height adjustable feature in the headlights.
Other than that, all body pieces shoudl be nice and easy. I had considered something like this since I liked the old body style on my 2002 better as well, but decided it was not feasible or easy anough for my tastes
good luck though!