I'm afraid the FSM is no help on this, because they assume you'll just toss it. You probably won't know just what you need until you open it up. In some alternators, the bearings will slip off the shaft and stay in the case, making replacement very easy. Just punch out and replace. Keep careful track of any shims or spacers. On others, the bearings may be pretty well pressed onto the shaft and require pulling, heat, etc. to remove. These still shouldn't be too hard to put back on if you can get the old ones off. Try not to hammer too hard on the shafts, etc. I once toasted a very expensive Paris-Rhone alternator when, attempting to hammer it apart, I found that the field winding was a press fit on the shaft, and, well, it moved and I paid for a new alternator.
You will also probably want to renew the brushes if you can, and if the brush holder doesn't mount externally, you'll have to study how the brushes are held open when you reassemble. The old Delco alternators had little pinholes in the case so you could stick a couple of little pins in to hold the brushes out, but they all differ. I don't even know what brand would be in your XJ. Resist the temptation to sand the slip rings. Clean them if needed, but use nothing coarser than crocus cloth.
Pity yours is a 98. I have an 89 alternator in my spares, and we could have swapped.
