It's all the same from all years, Plug and play.
However, I have seen many people doing different shits when mounting 99-00 bumper on the 96 body. Some just cut the bumper horizontally around the number plate area to mount the lower portion of 99-00 on the existing 96-98 bumper. It's easier to change it back under such case, just plug and play back.
Some people actually use the 99-00 completely with 99-00 grille, but make some filling on the hood and headlights area to force the 99-00 bumper goes on it. If that's the case, you are doomed.