As you say, it is definitely not the Chic. This one is much more rounded, and very reminiscent of the tailpiece on a Triumph Thruxton. Cool little built in taillight, as well.
I don't think it would be TOO hard to DIY (in my head)...strip the stock seat pan, cover the tank in Saran Wrap, use the rearward ~foot of the tank as a mold to create the hump shape out of fiberglass, enclose the hump, cover the remainder of the seat area in flat fiberglass, sand, paint, get an upholsterer to fab up a leather seat, drill a 2" hole in the back and wire in a generic tail light. That's ALL.