From the best we can tell, the 2013 Legacy updated front end fitment to the 2010-2012 Legacy would involve bumper cover, grille and your choice of fog light or fog light blank panels in the lower fascia. Headlight fitment is the same, however, some of the 2013 headlights are blacked out.
This has not been confirmed by anyone actually doing it, this is just the supposed parts list so far. And this is USDM models. This fitment to an Outback is likely but has not been contemplated or confirmed.