Ummmm ...
What year is your XJ? Does it have "Command-Trac" or "Selec-Trac"?
Up through 1990 the Command-Trac XJs had a vacuum disconnect on the right front axle shaft. The transfer case itself does not use vacuum to engage or to disengage, and the HUBS are not locking/unlocking (automatic) hubs. There were never any XJs sold by the factory with manual locking hubs.
The transfer case used with Command-Trac was the 231 from 1987 and up, but prior to 1987 it was a 207. There were other transfer cases used as "Selec-Trac," which is why we need to know what year your XJ is before giving a more definitive answer.
Sounds like you've been given some slightly confusing and incorrect information so far.