Its an 02 with a 7.3 I just finished the 07 Harley Edition front end and the 08 Tailgate and Rear bumper. I even have the back up camera in the tail gate handle hooked up.:beer:
You have to take the over load springs off to lower it more than 3 inches in the back. So what I did was install helper spring air bags to make up the difference. I don't have a goose neck trailer right now, but I plan on buying one in the future, right now I pull a 24' tag trailer. So the answer to your question is none if you buy the right parts.
Thanks!