Likely this was an opportunistic design. Where the airframe was available at the right time and place and an astute individual made it happen. I don't think the specifics of the airframe itself matter. It's a fuselage with a ramp. Close enough. But pretty cool none the less.You think it would be a CH-47 rear end all things considered, not a CH-46 one. That's a nice training facility. When I was at PMRF Barking Sands back in the late 80s, we used an old tower to practice rappelling.