An 8.8 out of a Ford Explorer is another good choice. It has aftermarket support to help you put it under a YJ. The later years are 31 spline and have disk brakes with parking brakes. It has the correct wheel bolt pattern and is just slightly narrower than the stock YJ axle. Some people run 1" spacers. Some do not. With a little searching, you may even find one to match your front axle ratio and/or with a limited slip.