Rear End

First thing is to look at the picture below and figure out which rear end you have for sure. Best way is to start counting bolts on the cover and comparing shapes. I believe the 7.25 also had a 10 bolt version that was more octagonal. Best hope is you have an oval (8.25 or round 8.75)

If you have the 7.25, I would start looking for something bigger.
Good luck.