When I trimmed the ends of the Sissy, I took 3/8" off the inside and flattened the bottoms so that they would be pointed slightly to the center.so the would mount correctly to the studs welded to the frame.
I also found these offset banana brackets I made for a build years ago out of the MetalChewy parts bin for the sissy to angle backwards from the seat. More Polishing required for use...
Great work on the seat and nice looking bike! A lot of cool details. The wheels, the crankset, the chain and that rear hub with the big cooling disk work great together. Handlebars, grips, brake levers, shifter... Very nice!
I would adjust that stem to be low and close to the fork spring. Following the line of the top tube.
What's the idea with the BB adapter in the rear BB housing?