The 94 has no voltage regulator in it - this is handled by the engine computer. XJ's before 91 have the regulator in the alternator, so I would expect you will not be able to use a pre-91 XJ alternator unless you modify it. Belt layout changed in 96, and I haven't really looked closely to see if the mounting differs in any important way (I'm not at home, or I'd go out right now and look at the 99 and 95 side by side). 91-95 would be the best bet for a no-hassle fit.