Thanks for those pictures. I also looked at the website folding explanation, and I see how they work it. I was just planing on making it come appart, but the way they pivot it certainly keeps the chain mess down, and is pretty simple in execution.
Materials wise, I can get 4130 in all the usual sizes. And can turn any special parts that might be required. But I haven't even given any of this much thought yet. The holy grail would be a totaled frame, I guess if one really wanted to rip the design off. For myself I would be pretty happy just winging it. But you can't do that if others are involved.