Bigger Rearend in my duster

Where did the rear come from and what is it? the measurement you have is wrong between the 2 series of joints, there is more than .25" difference between 7260 and 7290.
If you had .50" difference then you have a different joint, most likey you have the same joint and just have a casting difference or you measured one yoke across the middle or bottom and the other at the top.