That new lower valence looks insane! I just recently did the 96-98 bumper swap on my 99. Everything went together smoothly, with the exception of having to sawzall out the side bumper bushings that attached to the body. In addition, I noticed as soon as I installed my new bumper (96-98) with the fogs disconnected (96-98 didn't have them), that I was getting hyperflash and that the signals wouldn't work. I ended up replacing my turn signal relay and new bulbs to make it work again. I used my 99 bulbs and sockets in the 96-98 with some cutting of the housings. The 99 have 4 small prongs like the 96-98, but are a little larger and therefore didn't fit the 96-98 housing without modification. I should also recommend using an additional rubber grommet if you plan on using your 99-02 sockets in the old housings, as if not used they will wiggle like crazy.
Hope this helps someone who runs into this in the future!