Have you seen the LMT Monolithic Rail?
I can't remember who makes the example in picts 1 and 3, but I've seen them. I think it's actually a free float tube and a rail that attaches to the upper and contacts the free float...they're not one unit.
The middle one is a (enter company, I don't remember) free float 4-rail Monolithic "Look" hand guard.
What do the experts think? Am I close?
The first and the last pics are bushmaster carbon 15s. The middle is a S&W M&P-15