I had to Helicoil my 98 front knuckle. The Helicoil kit size is 5/16-18 and the kit number is 5521-5.
Then get the replacement caliper bolts at autozone or parts america for your XJ. They are cheep.
Word of caution: make sure you drill and tap that hole perfectly straight.
If not you will have one hell of a time getting the caliper bolt back in.
I did mine and drilled it just a hair off level, and it was a PITA getting it back in. Oh, it went back in, but I had to use all my strength to get it screwed in there.
BTW....its still holding too.
Helicoils work great.