Not sure how much bolt length the saddlebag brackets are taking up, but here's what I'd do. Feel the ends of bolts 14 and 16 inside the fender. If there is approximately 1/4" extending past the nuts, and the sissy bar brackets are only 1/8" thick, you should be fine with the existing bolts. If not, find some slightly longer bolts. Bolts that are too long can rub the tire, and you don't want that.
Thanks for the helpful response, Flite.
My concern is with access to the nut (if needed) for the rear bolt. I believe that bolt does not go through the fender, but only the tail plate. I can't see behind the plate, and hope that the bolt is going in to a thread in (or fixed to) the plate.
If there is a separate nut hidden behind the plate, I fear I would have to remove the plate, in order to get a hold on the nut. I'd then have to tighten that bolt fixing saddle bag support and new (to me) sissy bar bracket, before reinstalling the plate. Of course, I think that removing the tail plates would involve disconnecting or removing flashers and shocks. (At that point, I have to question how much I need or want the sissy bar, or at least how urgent it is!)
If you have seen the back of one of these (2nd gen) tail plates, maybe you have an idea about how that rear bolt attaches? (There are also two holes close together on both the tail plate and fender behind this bolt position, used for the flasher bolt and wiring.) I can't get my eyes or fingers behind the tail plate to see much.
Thanks, again. Appreciate your wisdom!