Interested in legacy and impreza's 1999 to 2010 models, engine and gearbox interchangeability.

Guessing the engine is pretty much the same in all of them, so if i take an impreza engine i can stick into any legacy without a problem ?
Not really interested in getting a legacy engine into an impreza so no worries there

What about the manual 6 speed gearbox though, is it the same in all of them too ?