The next issue that comes up is the alignment. The GD has a wider track than a GG, which comes from longer lateral links and control arms. This changes the geometry slightly and the angle of the mounting holes on the bottom of an 02+ Impreza sedan strut. This basically means that if you put Impreza sedan struts in a Legacy, there will be less negative camber. The most camber available seems to be about -1 degree in the front and it will be about half a degree positive in the rear. However, the difference between the cars is not simply an issue of track width. There is also a slight difference between a GG and the Legacy, so the angles of the holes on the flange on BC, GD, and GG struts are all different. I suppose it's all close enough to get away with switching things. I'm sort of working on figuring out the exact differences.
This is one of the closest references I could find but it doesn't really address BG/BK wagons.