Have you made, or do you know of any versions including the shell bracket at the bottom? If not, is the plain rectangle at the bottom the backplate for the shotgun cartridges, to which I could add a bracket of my own?
I had a look in theatre, and I'm certain the vertical rectangle connecting them is something like a fabric strap. I'm going to use something like seatbelt material if I can find some. It also passes throught that middle metal buckle, rather than having an open space there, so it definitely seems like a belt of some sort should pass through all the pieces.