Not a seat expert, by any sense of the word, but that looks like a old, recovered scorpion seat, from the 60's or 70's. Not to mention, that I may have the name wrong. But I had a 72 XLH, that had a seat that same shape, but with diamond stiching and buttons at each intersection. The tubing for the sissy bar, unless you get something indestructable, would not work. The longer you make it, the more likely it is to break. Even solid round stock, is not hard enough to take the vibes. It has to be something high carbon or moly. Short, grabrail type sissy bar, may be ok for the tubing, but I sure would not want to have that thing break off and stab somebody in the leg, or front tire. Maybe somebody can give you a more technical answer than mine.