I did this conversion to my GN. In order to do it like factory, you need everything, and I mean EVERYTHING! I got lucky when I got mine as I had a guy pull an entire setup off a low mile grandma driven regal. Anyhow, let me start with the parts list:
AC Box
Ducting behind the dash. There are 2 pieces, upper and lower (yes it's different than AC)
Wiring from behind the dash(I never got this so I had to use the wiring diagram and then cut/splice)
Vent/Control Switch panel
Vent cables and handles that go directly under the steering column and across to the box
cowl screen (again, different than AC)
Dummy vents (for the far left and right sides, only the center of the dash has a vent now)
If I had to do this again, I would. However, I would only do it just before an engine swap. I had the passenger fender off when I did mine so it was MUCH easier. You also have to pull the dash to remove the original ducting, but contrary to what I have been told, it wasn't that much of a pain in the arse. Any questions, feel free to PM me.