From what I’ve gathered in the last, the difference is in the bearing design but not in the shoulder height. Something like one is a roller design and another is a tapered roller design. It would be helpful if Wilwood would specify which one is needed but it sounds like maybe bothering pre and post 99 will work. The only thing that needs to be used is the 84-89 HP D30 knuckles because they had a bolt on caliper vs the floating caliper with the brake pad “wings” of later years. They show the knuckle as just 87-89 but that’s not correct. All the different unit bearings fit that knuckle though. If the above two unit bearings work with the Wilwood kit then I just wonder about the 99+ unit bearings. They also have slightly longer wheel studs