If you are swapping out the complete third, then you just have to find one with 4.62s and if yours had rear ABS (it will have an electrical connection on the third), then you will need to find one that has the electrical connector...otherwise, your brake light on the dash will be on all the time. If yours doesn't have the electrical connector on the rear third, you can either use one with it, or without it.....it will work and fit fine and it won't affect the brake light on the dash or anything else.
Any 89-95 2 door with an 8V and an auto should have 4.62 gears.
All 96-98 X90s had 4.62s (both auto and manual trannies).
The 91 4 doors with the auto tranny had 4.62s.