Transmission HELP

Hi, I am in search of a replacement transmission for my sons 95 SVX. I believe I found one, used since the car is not even paid off and he certainly cannot afford a rebuilt one. Well heres some questions I hope you can help me with. Before buying the Trans what are some questions I should know about it? (besides warranty which is 90 days.) Also I have been looking around and am not sure how good the 3 top trans mechanics around my area are on working on Subaru. Is there anything I should definetly have replaced that corresponds with having a trans put in? I don't want to go into this not knowing what I should have asked. (just taking for granted that they knew exactly what they were doing.) Sorry for this being so long I just don't want this to end up being a nightmare afterwards. THANKS in advance for all your help !!! Diane