It took me awhile to assemble part#'s and thought I'd share them so if anyone else contemplates they have them at their finger tips.
A couple of "heads up". The GC8 (older style WRX) aluminum control arms fit the WRX wagon w/ a few minor differences. First the front sway links- I originally ordered the GC8 front sway links (pillowball type), but found they were too long. I ordered the new (GD) WRX sedan ones (pillowball type) and they fit just right.
The other difference I discovered was the front bushings (already pressed in when you buy the GC arms) are 55mm wide, the oem ones on the wagon are 61mm- when putting the front bushing portion of the arm in I noticed slack in the bracket in the cross member. I found thick steel washers that took up the slack on each end.
You can get all of these parts from your dealer, the cheapest way to pick up a set though is to find takeoffs from Japan (where they had GC WRX's).
There are several parts you can reuse if you choose to- balljoints (you do need the "sleeve" that is shown in the diagram however, as well as a washer that goes between the castle nut and the aluminum arm), the rubber spacers around the rear bushing, the rear bushings themselves- however I'd reccomend the Grp N ones- if your going thru the trouble to replace arms, you want better bushings (those are the part#'s I list for those).
I'll be writing up a tutorial on aluminum control arm install (would apply to wagon or sedan) this evening if I get a chance.