Chall08

Is there any way of telling exactly what year model(s) xj my axles came out of ? Either by way of numbers or certain characteristics or any other way you may know of. Btw they're under an 87 4.0 4wd MJ. I started putting them under it about 5 years ago and never finished the project so now I'm back at it. Right now I'm a the point of buying rotors and pads and I can remember what year model these axles came from. Any help will be greatly appreciated.