I'm not that familiar with YJs. I think you have a Dana 30 front axle, and that will probably need a different carrier for 4.88 gears. I had to get a different carrier when I went to 4.56 gears.

Re the rear diff... I haave an AMC20, and the same carrier worked for 3.08 through 4.56. But I think you probably have a Dana 35 rear axle, so you're probably going to have to get a different carrier for the rear, too.

But think of it this way... As long as you have to get different carriers, forget the carriers and take this opportunity to install lockers in both axles. Be sure to get lockers that replace the entire carrier. The two most common lockers in that catagory are the Detroit EZ Locker (an automatic locker) and the ARB Locker (a selectable pneumatic locker). Were it me, I'd put the Detroit in the rear, and put the ARB in the front. That way, you can still use 4WD on the street when it snows.