If it's a Denso alternator then it should be a straight swap. The build sheet for my 1998
XJ said that it came with an (optional) 117A alternator from the factory. The previous
owner (or his mechanic) replaced it with a 90A alternator, and I had unknowingly
replaced that alternator with another 90A alternator when it went bad (bearings).
After I read my build sheet, I made sure that the next replacement would be a 117A
alternator. When this happened, I set the two alternators side-by-side and I could not
tell any difference between them. Same length and diameter. Same wire connections.
Same case vents and ribs. It went straight in. No fuss.
One day, for laughs, I got a 135A Denso alternator from a WJ V8. There is a very noticeable size difference here. The mount bracket needs to be filed a bit, and the
plastic connector insulator needs to be swapped with the one from a 90A or 117A unit.
Also, the belt pulley needs to be swapped with the one from your car as it has an extra
groove. I have not installed it yet, but I have everything ready to bolt in when the
current 117A alternator eventually goes south. Some folks upgrade the cables
when doing this, but I don't have any power-hungry light bars, or winches, or big
stereo amp, and so I'm thinking of staying with the OEM wires and see how it goes
from there.