Quick update, for those interested. I took this to a local framer I have worked with before, and we (carefully) cracked it open.
There were three layers of foam board, with the board used to float the art attached to those. The outer layers of board looked like a different type than the inner layer, but the inner board and the board “attached” to the page were determined likely to be made of archival materials. The page itself was attached with what appeared to be archival tape: two pieces along the top, two on the sides, and two along the bottom. If I had thought about it, I would have taken some photos. All in all, it was very easy to disassemble. A couple of the foam board layers do have to be removed (carefully) to get safe access to the tape holding the art to the floater board.
I wasn’t interested in keeping the page framed, so we separated the art from the board and that was it.