Hey Mike!
Seriously?!? How cool is that!
I've owned this since sometime in 2006. I seem to recall paying $375 for it, but it was entirely complete. Aside from a Halcyon facehugger, this was my very first true Aliens prop -- and a pricey one for me at that time. I cannot remember who or where it came from, or whether it was state-side or not. Unfortunately I've had a hard-drive or two fail on me since then, and much of my old correspondences have been lost.
What I do know is that I treated it like it was screen-used (because it surely looked the part), and never used it with my USCM costume. Instead I bought another shoulder lamp later that year from Matt -- a black resin kit -- used it at DragonCon that September, and promptly smashed it into several pieces the following month during a Halloween costume contest. I now believe the elbow joint from your casting went on to replace my broken one.
I'm struggling with remembering what happened to the original head lamp unit, because it was wired and lit up with either C or D size batteries.
So then... judging from the four little silver marks inside the casings, mine is apparently number 4 out of 5 then, right?
Do you know whose original shoulder lamp this casting was pulled from?