The computer won't work even if you only want to use 6 out of 8 cylinders.
Get a computer from an 89-93 5.0 Mustang. Forget about anyting else.
Here's a list courtesy of Steve89GT...
There are a few different varieties of computers... just a few different calibrations.. Here's the #'s of most of the MAF computers that are around. A9L and A9P are the most common.
1988 MANUAL 8LD
1988 AUTO 8LF
1989 MANUAL A9L, A9S
1989 AUTO A9P, A9T
1990-92 MANUAL A9L
1990-92 AUTO A9P
1993 MANUAL A3M
1993 AUTO C3W
1993 COBRA X3Z
The harness itself is what is different.. Most of the computers are interchangeable, although I have never done it.
You can also use an auto computer in a manual...
Steve