He's screwing with you.
99-04 Grand Cherokee knuckles swap on with the right combination of steering parts (options, here), lower ball joints (99-04 Grand Cherokee), hubs (2001 Cherokee), spacers (numerous manufacturers) and then you have two choices of rotor (neither one are a direct bolt on) and in the end, you have 5x4.5 bolt pattern just like original.
High Pinion & Low Pinion knuckles are the same.
84-89 (or is it 90? can't remember) use a different knuckle but if you match the hubs, rotors & calipers to the model year you pull the knuckles from you should be fine. I'm hazy on the early XJ stuff though so don't take this as gospel.
I've heard from some Chevy S10 forum reading that late model Dodge Dana 44 knuckles will swap onto a Dana 30 but haven't verified this. It's a weird option but I think it's an option.
Easiest thing, by far, is to run your LP knuckles / hubs / brakes (which you can do)