What you would have to do is source the wiring diagrams and ecu pinouts for both models and match them up to see what is different. The swap has been done by Scoobyslack1, however he paid a local Subaru mechanic to do the swap and wiring. Aside from the wiring, everything would bolt right in from the crossmember to the tranny.
Just so you know, the Legacy turbo's are very hard to come by. If you find one, count your blessings.