you don't need a whole new axle to fix a brake squeak.
swapping to late model unit bearings and rotors will give exactly zero benefit vs your early model unit bearings and rotors.
you just need to know what you have - if you have an early style setup, then order parts for a 98. if you have late model setup, then order stuff for a 2000+. the guys at parts stores don't know the difference, and if you tell them you have a split year of 99, you get whatever parts the inaccurate computer tells them to give you.
figure out what you have - late model or new model, buy the correct parts for it, and use the proper brake lube when you put the calipers back on. check for divots, and repair them with a welder if necessary. there's a write-up on jeepforum.com.