See your IH dealer. There are 2 different ones for the 7.3 DI engine, they changed in 98...

From Ford:

Try F4TZ-9D30-K UVC early, F4TZ-9D30-AB UVC late,F7TZ-14489-BA UVC repair kits early, F4TZ-14489-AA UVC repair kits late. Login to read more.