I would use the explorer setup, and get a mustang harness and A9L cause it will be easier to trim down then the explorer unit.You seen my car it's not that hard to do
same boat You have to use the stock computer from the explorer. No cost short cuts here! The ecu controls both the engine and tranny, cost for a stand alone 4r70w controller runs about 650$(computer,wires,sensors) Best way is running the stock computer with the system. I'm stalled on my project because of this. I own a built 4r70w which means either I'm running efi or buying the stand alone system. After I factor in the cost of carb and buying the system I'm over 850$! For that amount I should be able to convert to efi right and still run the tranny using the stock computer. Just way more of a headache. forgot to mention that the 86 mustang has a functional speed sensor in the tail of the aod for both computer and cable speedos. You should be able to swap over the standard aod tail housing and gear to the 4r70w then just buy the sensor.
Holley makes a controller that bolts onto their carbs to run these transmissions now. It costs about $125