There are NO kits available to do a front diff drop on a KJ, a few have done it but if you keep under a 3.5 inch lift you should have no problems. The CVs will and do go bad, esp the right side with the intermediate shaft. The shaft starts to rust, it can not slide back and forth and then you have noise and then they need replaced. All part of owning any 4 WD drive. With all the moving parts things wear out, go bad and you get to spemd money.
Oh I assumed you were talking about the CVs since you mentioned the right side and not the front driveshaft which also has problems of its own. Check the rear boot every oil change they like to wear out and cause problems as well
If they suggested doing a diff drop I really wonder how much they know about Libertys??????
I haven't looked recently but I think JeepinByAl (thanks jeepinjarhead)

did have a diff drop but still you should not need it.
I ran mine for over 98000 miles lifted with no problems, and then had to replaced the right side CV due mainly to rust on the splines causing noises.