Courtesy Al Gainey & Alex Shikhmuradov.

Tools required:

3/8 drive ratchet
Deep 14mm socket
Standard 12mm socket
Open end 12mm wrench
Standard 14mm socket
Open end 14mm wrench
Standard 17mm socket
Various 3/8 ratchet extenders
Can of WD-40



Use a floor jack and a piece of wood and jack up the frame of the car just behind the front wheel. Jack the car up as far as you can. Put a jack stand there. Now jack up the rear frame just in front of the rear tire. Put a jack stand there. One side of your car should be up in the air now. Which side is up to you, as long as you can slide under the side that is jacked up. Subaru uses an elaborate tranny crossmember system. There are two crossmembers, one long one up front, and one short one towards the rear. In between these two crossmembers is a third crossmember that runs parallel the the trans.

Remove the four 14mm bolts that secure the tranny mount to the bottom of the tranny. On this picture you can only see one bolt. (#1 on the picture below) The other one is right after it towards the front of the car and then the other two symmetrically on the other side of the tranny mount.

Now remove the two nuts from off the studs coming off the bottom of the tranny mount (#2 and #3 on the picture above). Loosen, but do not remove, the two bolts in the center of the rear crossmember (#4 and #5).

Remove the two 17mm bolts from the front (long) crossmember where it mounts to the floor of the car. Don't worry about the Tranny falling on you, it won't. The tranny mount should almost fall out of the car.

This is how the stock tranny mount looks comparing to the STi piece.

Installation is in reverse order. It might be slightly difficult to align everything so that all bolts/nuts will go in place. Just be patient and you'll do it.