Ifound a aod out of a 88 or 89 5.0 i cant remember the year itwas one of those. Is this the one that dosent have a computer? Basically will it work.

 

88 and up AODs were better than 87 and earlier.
Mustangs were computer controlled starting in 94.
It will bolt in and work if you know how to hook up the linkages correctly.
You'll have to fabricate a crossmember or buy one. The speedo cable will be too short. Long tube headers won't fit unless modified. ( I used shorties last time I did this swap.)
Use the slip yoke that came with the AOD and check driveshaft length

 

Dont forget the TV cable!! Hedings 2& 3
http://www.becontrols.com/tech/tech.htm#topten_q2

 

you might want to build it up a little i have exploded a few aods in stock fox bodys before but i got a lead foot.later on you might want to regear your rear end to a 3.55 or 3.73