Why don’t my new U joints fit? (Solved, thanks!)

Replacing the U joints on the E body, 8.75 rear end. I have the small 7260 joints up front and a universal 7260/7290 at the differential. I ordered Neapco 1-6301 for the front and a Spicer 5-789X universal for the rear.

The cap diameters are correct, but when I go to press them in, the lock ring grooves are too wide apart and I can’t get both sides inside the flange of the shaft to get the lock rings on. The inside diameters on both ends of the shaft are 2.125, and I’m getting almost 2.250 on both new joints. I’ve tried the Moog 347, same measurement.

What’s going on here?
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