I have a BUIS that came with a rifle I bought. I had given up hope in identifying it and forgotten all about it until someone posted a pic of it on TOS asking the same thing and no one there could identify it. It rekindled my interest in finding out more about it. I have more confidence in the people here. 
Here are some pics of his BUIS:
looks to be an early prototype of the GG&G MAD buis…however it is pretty crude in comparison…got my interest:)
It does remind me of that, but it only has one big aperture. If you look at the aperture it appears to be adjustable vertically and is locked in place by the screw. When I remove the screw I can slide the aperture up or down in the housing. But without the capability for fine repeatable adjustment it doesn’t look like an elevation or range adjustment.