According to the years you gave me, this makes sense then, as far as the years go. Listen to this.
A good friend of mine and myself were looking at an '86 xj he just acquired from his Dad, a hand-me-down. His Dad bought the thing brand new in '86, we remember the day he brought it home. It came with the four cylinder engine, yet we just realized that it has always had a "2.8L V-6" emblem on the lower edge of the rear hatch. Its been in the family 'till this day, never been messed with, just always been his Dads work vehicle. Dealer goof up, or maybe factory goof up?? Interesting, if anything.