There are actually a couple threads on this forum about it. You’ll want to spend some time searching.
I believe the DC body mounts won’t line up on your 99 frame. Specifically the rear ones. The 2 at the core support and 2 under the front of the front doors are the same on all of them.
I’m currently waiting to pull the trigger on a new (used) cab so I’ve done some reading recently. I’m on my phone or else I’d share the threads I remember seeing.
Mine will probably be less complicated than yours because I’m staying with a single cab.
I’ve read there are pretty big differences in wiring (both engine and body) after the 01+ refresh.