Okay, so many factors here. The 98 was a one year model car, meaning fuel pump upgrades are a 98 only deal along with many other things. If you are set on using the 5.0L you have two options.
Option 1:
Swap out everything, all wiring, K-member, Fuel System, everything from a 94/95 GT/Cobra
Option 2:
Swap out a lot of the wiring for a 98 GT wiring. You still need to swap the K-Member. Then you'd need to modify the wiring to work with a 5.0L Explorer setup. That setup was OBD2, so has all the "needed" sensors to work. This way you could use the Mustang GT (4.6L) Computer.
Now those are high level overviews but should give you an idea. Not saying its impossible to do, but will require a lot of work. I have done them many times.