I would put the U-bolts on top of each other, and see if they are both the same. It is possible one was made wrong or packaged wrong. The U-bolts for a 7 1/4 are smaller than for a 8 3/4. Definitely do not take material off the axle tube
Here's a second to that idea. Something somewhere is wonky. You should not have to apply force to get this stuff to install. Figure out what you have before you grab a bigger hammer.