I'm glad you thought it was level headed thinking. I hope everyone else did or, at least, a majority of them...
To run a 4R70W with the computer from the original car, you would have to hook up all kinds of sensors to make it work (air temp, O2, MAF, TPS etc)plus have to disable others like the fuel injection system. It would be a huge electronic task. That is why Baumann and others came up with the TCS and Optishift modules.
The AOD's came in many Ford and Mercury cars from the late 80's early 90.
The "best" AOD would probably be from a 93 Mustang GT as that was the last year for it. The GT would probably have the better valve body too. At least try to get one from a 89 or later car as they have the better VB in them.
Speaking of valve bodies. Lentech, Baumann, Broader performance and others sell them. I myself have a Lentech. It has been great. I did manage to play with things and mess it up as I tend to play with things a lot. A few calls to Len at Lentech solved my problems. If I would have left it alone, I would have been fine...
Mine uses a 1,2,3 shifter pattern. With 3 being full auto with 4th gear (unless I click the 4th gear switch).
There are many shops that will rebuild and beef up your AOD. Also many shops that will sell you one that is already built and ready for punishment.
The weak part of the AOD is the 4th gear band. You don't want to ever go WOT from 3-4. Lentech, and others, have a switch that let's you lock out 4th gear so you can't do WOT shifts. I have that for my trips to the drag strip
There are other weak ares of the stock unit so if you buy used, have it built up for reliability.
Depending on how much you pay for a used trans and how much it cost to get rebuilt, then modded , you may be better off dollar wise to buy one already built.
Here are a couple links to places. Granted, there are a lot of places. This is just a sampling.
Broader Performance prices from $1100 to $2000.
Lentech Street Bruiser has the wide ratio gear set. Item 7000-AOD-STB $2495
I don't know anything about this place, perhaps others will chime in.
Here is a link to A LOT of info.
Good luck with your choice. It won't be easy.... but never is...
Of course, these are my opinions, others will vary.