C4

The C-4 came in 3 different torque conv. patterns, bell sizes, and flywheel tooth counts. Therefore your bell/flywheel/convertor bolt pattern must match. The good news for you is the largest of the 3 C-4 set-ups is the same as all AODs. If you can find a C-4 with the 11 7/16" spread across the convertor studs it is a bolt in for your AOD.

With the large bolt pattern C-4 convertor {11 7/16"} the flywheel is the same as the AOD. I think it is a 168 tooth? {maybe 164?} flywheel. On the next smaller C-4 convertor {10 3/8" stud spacing} I think the flywheel tooth count is in the 150s {157?} and the teeny Mustang II {only} convertor flywheel is in the 140s {148?}. Each of these convertor/flywheel combos have their own different bell size and you cannot interchange them. The starter is the same on all of them as the corresponding bell hsg. spaces the starter correctly for each one of the conv./flywheel combos.
The larger C-4 set up is commonly found in Ford trucks and full size big cars and wagons.
You will find the big pattern C-4 offered in both the pan fill {dipstick screws into pan} and case fill versions {dipstick presses into case right front of the pan}. If you find a pan fill C-4 it will have the big pattern, same as AOD convertor set up. Also the pan fill C-4s have the bell attached to the case with a seperate set of bolts, not sharing the front pump bolts to attach bell housing like the case fill C-4s do. They {pan fill} are considered "stronger" than the case fills even though the internal components are nearly identical. Either one will work and can be beefed up nicely for your needs. Stay away from the C-5s offered in the early 80's cars as they have a lock-up convertor that has a slightly longer bell to accomodate the thicker lock up convertor and are big pattern too. You want a 70's model C-4 to build for a hot street or strip car.
I think the gear ratios are close to the AOD or better for racing. Obviously they are 1:1 in high gear, same as 3rd in the AOD. You will lose the overdrive!

your stock shifter wont work with the c4 pattern. i believe there is a kit that you can use so that it will work or you can just buy an aftermarket shifter that will work with it.

Yes, if you get all 4 {bell, flywheel, block plate & convertor} from the same small block Ford car it will "bolt up" to the back of your 5.0. You still have to deal with trans mount/x-member differences, shifter differences, cooling line differences, driveshaft differences and be sure the flywheel you get is the correct 50 oz. balance for your 5.0 {I'm assuming it is a late 80's Mustang302}. Drive your present AOD around in "D" {not circle D} to get a feel for what the C-4 will be like.

Here's a listing of Ford automatic trans ratios,
except the OD for the electronic wide ratio AOD
(the 4R70W) is incorrectly listed as .67 like the
AOD. It should be .7.

http://www.thepontiactransampage.com/transgears.html

The C4 takes significantly less power to turn, so you would gain some there with a C-4.

However, you lose OD, if that's important.

You would also have to have it beefed up some
if you're going to put it behind an engine that's
been modified to any major degree.

Just FYI, here's some info on beefing your AOD,
to hold various levels of power and abuse, and
info on another option, the wider ratio 4R70W.

Also, the wide ratio gearset from later model
4R70Ws can be swapped into an AOD along with
quite a bit of the other improved, stronger internals.

Not as good from a valve body shifting control
standpoint, but can be done fairly cheaply if you
get a decent used later model 4R trans.

http://www.lincolnsonline.com/tech/00111.html
http://www.lincolnsonline.com/tech/00080.html

Good luck.