I am not sure about subaru's, but with other vehicles there are specific tooling you will need to shim the Diff correctly. I had to borrow a bunch of stuff when I did my last job. It was a rear diff. and I had to take it apart 3 times before it was shimmed correctly. If it were in my tranny like a subaru it would be a complete nightmare taking the tranny off and on that many times.
Call Solid they will hook you up. They do good work.