Impreza boxes are interchangable, the later boxes have an extra 4 bolts in the bell houseing witch you dont use as you wont have threads in your block, There is only 1 slight issuse,You have to modfiy your lower starter motor bolt, as yours has a stud an an 17mm headed nut. The later boxes have a hole where a bellhouesing bolt would go though witch you cant use.
As mention make sure you have the right matching diff
