Manufacture Date, Early '04

I know that the EGR design along with a few other things changed halfway through the '04 model year. What is the build date of the switchover? I am looking for a F-250 and would like to stay in the 2003-Early 04 engine if at all possible. I ask about build date on every truck I inquire on, but I cannot recall the actual date attached to the switch over. Can some one please advise....