Thanks for your comments NEWHD74FAN. The girl at CavalryCustoms was helpful with respect to giving me info on their BR2, distance between the sideplates at the docking points (10.5") & distance between the sideplates where the sissy bars enter (8.75"). This is fine, except of course I don't know how far toward the rear of the bike, the sideplates reach, ie, whether the sideplates takes the upright part far enough back to clear the overhang of the Sundowner seat. I guess the only way I'll know for sure is if someone out there already has this setup, unless I ask CavalryCustom to try one for me.