OK, found them.
The center "tube" is a solid bar to the point where it becomes a "socket" at the rear. It is still pinned into the stock Reese Tow Beast. The extension is not welded in any way to the frame OR to the existing Tow Beast. It's bolted in, with bolts/nuts that go in opposing directions. If I were to remove it, I'd have to pull the bolts, the pin, quick disconnect the lights and the 7-way and remove the air-valves from the angled pieces. Those air valves are emergency fill ports for the rear air-bags....I can turn a cutoff right there, and then fill if I had a leak in one or both of my air systems that can fill the bags.
There was one screw up in width which meant he had to put an additional 1/2" (I think) of plate to fill between the frame and the extension which makes it look a little rag-tag but is no less strong.
The Tow beast was already modified some when the Kelderman Air-Ride was put if I recall right, it is now an integral part of the suspension pieces. In other words, the Tow Beast can't be taken off without removing/releasing the rear spring mounts.
The rear-most cross piece is back to back channel, and the 7-way plug will be recessed into that cross bar (along with a giant DC hot/ground connector) so that the "shelf" will be completely flat and can hold several of the platic totes that carry various gear.
I can't seem to find one of my extension that has the over/under receivers, but you can see it in this photo where the "X" of plate steel kind of shows up. I was experimenting with loading ramps and such in this photo, but you can see the height of the bike above the "normal" hitch height is. I have a long tube inserted in the lower opening to use to help test load. May be hard to see this one very well....