I've got three brick structures with adjoining walls. At some point in the
last 110 years, an unknown joker decided that he wanted to add a couple of
doorways through the common walls. Rough holes were knocked though the
walls never being properly braced or supported. Amazingly, there aren't yet
any stress cracks or related structural damage but I don't care to press my
luck.

The walls are 12" thick and approx 3' wide. I'm guessing that I need to just
knock a few more bricks out across the top and add some horizontal wood
supports. My question is what type of wood is appropriate here. I'm sure
that the typical HD 2x12 pine plank is totally insufficient for that type
of load. Any thoughts?

-BB