I think that the Bullet frame presents a more difficult challenge because the frame lacks the straight line from the tank back to the shock posts, and instead drops low, more like a hardtail. This creates a special visual issue that most of the bikes like Triumph and Norton and Rickman didn't have to deal with. It has that triangle area under the seat that makes it harder to get a smooth line there.
The sub-frame for the C5 OEM pillion seat provides a very nice platform for seat and cafe modifications. Maybe you could consider fabricating something similar for your Bullet.
Looking good!Love the alloy tail section!