Just wanted to confirm that an EA81 can be dropped into a late 70s Subaru (stage 2).

 

Ie, that the physical size, transmission (or housing), and mounts are compatible (in terms of mounting the motor) between EA71 and EA81.

The engine mounts seem to be compatible, but I've read that an EA71 car has the starter mounted to the top center and I know the EA81 is towards the top on the left side. You can swap in an EA81 transaxle, or I've read something about just swapping the EA81 bell housing onto the EA71 trans. You might also need the clutch and/or flywheel from the EA81. If you opt for the tranny swap, be prepared to make modifications to the driveline, shifter linkages, and/or the cross member.

 

If you search EA81 + EA71 + swap, you'll probably find a write up from somebody who's actually done the swap.