Hi,
'92-'94 Legacy were 3.90 FD ratio. That's the most important part.
However, if you replace the rear diff you can use any '90-'91 '95-'98 2.2 or 2.5 Legacy , Impreza, or Forester Auto transmission. ..
>>Caveats: you'll need to change the pinion flange on the diff to match yours....different bolt spacing.
>>>Flex plate needs to match up, too.
The 'seating' of the Torque Converter is also very important - search on here, and there are are a couple of seals on input/output (?) shafts to replace.
Also, if buying one from a used parts yard, it may have been sitting on the shelf - for a long time and the internal seals may leak once installed- and the shop may not warranty that.