I AM running an SVX rear diff but changed the r&p to a 3.90 to match my front diff and for the better acceleration. (BTW, the R&P from the 02-early 03 rear r&p fit the SVX diff). The diff housing bolts in with no problems except one.....you have to use SVX CV shafts...but wait.......the SVX rear CV shafts wont fit the Impreza hubs
figure THAT one out! I did it and no, I didn't change the CV end (can't...tried) Just find an LSD that has the same ratio as your front diff from an Impreza and your set. On my car, there is soo much going on that has nothing to do with the actual swap but in my case, had everything to do with it so, sometimes it's hard to seperate what needs to be done vs what I actually did.
Bottom line is, if you start with an AWD standard trans, the EG33 bolts up and forget about it! If you need an LSD, get one from the same source any other Impreza would....it's the same thing. The actual drivetrain (trans, driveshaft and rear diff) don't need to be touched until you start pushing what they can handle...@300WHP IIRC.....or you run a set up like mine.
One other tip.......cage the car! I got several reports from some VERY reliable people that saw the car twist from the viewing area.....probably led to my rear diff breaking.......juuuuust a sugestion for handling and parts reliability.