I had one in a 1991. They were used in YJs the whole production run = through 1995. . .
The year of the XJ alone doesn't mean it's a vacuum disconnect. Regarless of year, an XJ optioned with a full-time (NP242) transfer case had a non-disconnect dana 30. I've got a 1987 with a non-vac D30. . .
The "left over parts" comment doesn't even make sense. . . You really gotta look at the axle to know for sure. . .