Eager Beaver,
No design changes except things like cup holders.
First, is the truck you are looking at a gasser or Powerstroke?
The plow package was available on that truck if it is a gasser. Look at the door sticker and see what the front GVAW is. If it is 5200 or higher your alright. If not, you will need to get the "X" code front springs for it. You can order them from your local ford dealer for around $130 ea. Like Dino said, don't use blocks.
If it's a gasser, a bigger alt. and trans cooler might be needed. The Powerstroke comes with these upgrades standard.
The 97 mount will not work on the 99. The frame is completely different. The wirring harness will work though.
As has been discussed in this thread, if it's a Supercab with an 8' bed, it's a little tricky in tight situations because of the length. But overall I have no probs at all.
Greg