Rear bumper looks stupid with no end caps on my 97. Since I have no flares and trimmed wheelwells, the original end caps would look even more ridiculous. Will the 84-96 style end caps work?

 

it would probably look worse.
Cut and fold the lower quarters and be done with it or get a bumper that wraps around

 

i thought the same thing so i bought a new rear bumper from jcr offroad with side armor

 

I have a pre97 bumper on my 98 and I think it looks ok. You will need to fold the corner of your hatch to clear the plastic where it meets the steel on the bumper but only a little.

Edit: You will need an actual pre97 bumper they are different than the newer style. They bolt right on but are a little different.

 

After I cut my quarters and before I swapped to a custom bumper I used the bumper corners off a pre 96 XJ. I just drilled the holes in my 98 bumper where I needed to and bolted them on. I just mounted them a bit further out as to not interfere with the hatch.