There were several variations of the C4 so you need to make sure you match everything up. Mainly the bellhousing, flexplate and stall need to match. The one I have found to fit best in a fox is the 157t version. Ford never used a 157t flexplate on a 5.0 so you will need an aftermarket flexplate to keep the balance right. TCI makes a 50oz/157t flexplate for exacly this and it reasonable. The big bell 164t version can use your stock AOD flexplate but again I had clearance issues when I tried it and there doesnt seem to be as much of a variety of stalls to choose from with the big one. So I would look for a case fill with a small bell. There is actually a 3rd size but you are not likely to run across one since they are as rare as unicorn poop.
You might also need to cut the spot welds on your crossmember and slide it forward, I had to but some might not. Shifter will have to be dealt with unless you are crafty and can make the AOD one work. I have made stock ones work but not the AOD cable shifter.
All I can think of at the moment but Im sure there is more.