Lincoln Mark VII (V7) ?

The AOD will work fine,but the driveshaft will be too long.You can have it shortened easily at a good shop.It doesn't cost that much,or,check a salvage yard or E-Bay.

The long AODs were in Town Cars, Mark VII's, Crown Vics
and some pickups/vans.

Most other ones will fit, but you do NOT want a V6 AOD.
They've got fewer clutch discs in a couple of the clutch packs.

Check out the transmission dimension chart on the tci
trans website, they give the "regular" AOD dimensions
like for your Mustang.

Basically, the "long" ones just have a longer output
shaft and tailshaft housing. They're 1" longer overall.
If push comes to shove, you can put your Mustang
output shaft & housing on the Mark VII trans, but the
guts have to come out of the trans to do it.
If you don't want to do a rebuild/refresh or any upgrades,
that gets kind of involved unless you're used to working
on AODs. Would probly be cheaper to have your original
Stang driveshaft shortened than hiring someone to do
that swap. Should be the same yoke.
The Linc shafts had a heavy balance weight on the yoke
that I don't think the Stangs had cuz of the shorter shaft
and slightly different angle that made it unnecessary.

For info on how to upgrade AOD's from mild to wild,
and detailed info on parts interchange between AODs,
AOD/Es and 4R70W's, go to www.lincolnsonline.com,
look in the tech section under transmissions.