Not sure what the .50BMG casing reference refers to in this instance. A .50 "Browning Machine Gun" case is what most people would call the "bullet" without the full metal jacket covered lead projectile.
What you have, I do not know, but it almost looks like a wiring panel of some sort perhaps. There are eleven posts (or studs) and I can't tell if the posts have horizontal holes through them or not on either side of the panel. I'm thinking that an "11 stud" panel piece is not related to a supposed .50BMG setup (odd number) for such a small panel assembly.
Interesting that the panel proper does not indicate any wear on the panel mount flathead screws. Makes me believe that whatever it is never saw any real service. Screwdrivers are notoriously not "angle ground drivers" and thus will bugger any head with even a single use. Only specialized screwdriver heads are flat ground.
Any other markings or angle shots for us?
Otherwise assuming your assessment that it is truly related to .50s airborne architecture, here is a crude guess of for electrical attachment points...