Maintaining something 31" deep might be another issue. Especially if you can't get directly over it.
If you go with a reef, I'd suggest going shallow and jut out into the room. It would just be waaaaay easier to deal with and require no carpentry work. I can see one of these in that spot...
Neo Nano | Deep Sea Aquatics Custom Aquariums
It has a 24" x 24" footprint, is around a 30g tank with a 10g sump in the stand. I've seen one in person, and it's a sweet looking setup.
I just think trying to shoehorn in a big tank in that confined area is just a list of problems waiting to happen.