Have a 97 legacy with a 3.90 final drive, need a new tranny. Have the option of getting a 97 Impreza transmission. The question here is, both have 3.90 final drive. All the gears are a bit shorter ,The one Impreza has a 3.333 fifth gear, while mine has a 3.416. 
The difference being the 1.8l Impreza vs. the 2.2l Impreza had different transmissions. 
The 1.8l has all the same ratios as my legacy, the 2.2l has shorter gears. 
What if any difference would it make putting that transmission in my legacy. 
 

I recommend you to post this question in the "1990 to present...." forum here on USMB.  You will get more views and answers to your question.

 

Good luck,

Sam