I'm not certain as to whether or not the found part for the jet pack harness has ever been identified (assuming it wasn't just fabricated from scratch) but has anyone considered the possibility of it being the sissy bar from a banana seat bike?
banana seat sissy bar in Bicycle Accessories | eBay
I had been quizzing a friend of mine ( Collector2 on the Mercs site) about the harness because he thought it looked familiar. Since he's a diver we had, of course, been looking at the SCUBA and then at his suggestion of it being more likely the SCBA tank frame harnesses. I had thought last night that I had found an auction with the right harness and got him to add more pics of the frame ( here: MSA Self Contained Breathing Apparatus' SCBA w EXTRAS | eBay ) but then my friend, for reasons unknown, had the epiphany of the sissy bar.
Just an idea and like I said maybe you guys have already found/decided what it was, with the Wiki a PITA to find anymore I couldn't be sure.
Let me know what you think,