Ok,
Sorry it took so long and I do not have any photos but this looks to be pretty strait forward. The studs or rivets that the 99 venture has between the trunk mount bolts were all bolts on the 97 RSTD. It apeared that you would do as others have spoke about is remove the stud/rivets that line up with sissy bar mount and replace with bolts and probably a nut. Mayde when I have time and the parts I will do this and post photos.