Also, the service bulletins for Nov. of 28 showed several pages of procedure to convert over to the newer yoke and spring system. Many frames might have been converted at dealerships because there were complaints about vibration. It was not a required change, so no one knows how many were modified. A very different situation from factory recalls today. Also, the brake system went through changes, most evident at the center cross member when considering the frame. Possibly most of them were changed over the years. Think of it as an update. Maybe because of safety, driver satisfaction, or availability of parts after old systems were obsoleted. Just decide how correct you have to be, could these modifications be an upgrade? Decide, then go to Steve Plucker"s timeline and the service bulletins. I think one of your frames will do fine if it's in good condition otherwise.