Body harness

Alright so I started out with a 99 v6 worktruck. Put in a 6.0, built 60e, and converted to dbw. Also swapped out dash and interior harness to 03-04 which is also the same year as the engine harness. My question is, do I need to swap out the 99 chassis harness or will it work? Will I need to re - pin anything?

You should be able to graft the new harness to the old harness. A wiring diagram of your current truck is helpful as is the diagram of an '03-'04 to correlate circuits. I find the diagrams helpful in the grafting process.