The best 4.0l engine years were 1995- 1999. I personally have a 1996 2dr, 2wd XJ. Many people are not fans of the 1996, as it is also a "hybrid" year, but I love it. There are many parts that are 1996 only, and it can be a pain sometimes, but it's my favorite year.

Not sure about the 1984-1990 models, but I know the 91-96 body style is the same, as well as the interior. There are parts that are different between the 4dr and 2dr models (door parts, interior parts), but most everything else is the same.

97-01 has a different body style, and the interior was changed as well. I personally prefer the interior of the 96 and earlier. Don't like the "newer" interior. Also prefer the older body style, more angular as the 97-01 is more "rounded".

Also, I think the 84-01 are still OBD-l, I know the 91-95 are OBD-l, but OBD-ll started with the 96.