I may be wrong but you shouldn't need them. They are for the mod cars that have two sets. They are used when you need to trick/fool the puter into thinking they are working when u remove or add high flow cats instead of the factory set up. I am not sure on why they would be used on a 5.0.
Oh and b/c you asked here is a link. Took me a while to find it. All part Numbers should be what you ask for at your local radio shack. (if I found the same link that I used for my 04 gt. Cost like 10 bucks)
Yes you could remove the check engine light, but that would be a major bandaid and not fix the real problem. The idea (as I understand it) of mil's is to fool the computer into thinking that you still have cats on a car that really doesn't have them. Since a fox doesn't have an o2 behind the second set of cats you can remove them with no real effects on your computers performance.
The rear set of a o2's simply transmit a signal to the computer, it the signal is in range the computer does nothing, when u omit the cats the exhaust isn't superheated (as the purposte of cats is the heat the exhaust to burn off excess fuel) then the o2's get a different reading and flip the cel. By creating mil's you trick the computer into thinking the rear set is up to par or within the correct range at all times.