8.25" 3.21 Sure-Grip

Not looking to make this a discussion, but 8.25 rear axles are all 27 spline until '96, then they went to 29 spline.As far as I can see, the 2:45 gear ratio carrier is different from all the rest. I just looked into this because I'm doing an 8.25 rear for my '73 Duster.