The 2005+ Auto Mustangs have a 5R55S transmission.
You could probably make it work but is it worth it?
The 4R70W is a stronger transmission that will handle more abuse than the 5R55S. You won't much or anything with the 5R55S. I posted this before but here are the gear ratios for both transmissions.
5R55S:
1) 3.22
2) 2.29
3) 1.55
4) 1.00
5) 0.71
4R70W:
1) 2.84
2) 1.55
3) 1.00
4) 0.70
You will be able to launch a little harder due to the lower 1st gear, but you have an extra shift to deal with. The 4R70W will shift to 1-2 at the same MPH as the 5R55S shifts 2-3 at WOT and shift at the same point after that. It is track proven, the 5R55S does not have any performance advantage over the 4R70W.
There is no advantage of the 5R55S over the 4R70W once the 5 speed is in 3rd gear, in fact it will cost you a bit of gas mileage when both are in Over-Drive...