I am considering an engine swap. I have been looking for a donor car and was wondering about the transmission. I have an automatic '07. Does the donor GT have to be automatic or can it be manual. I really don't know how this works.

 

Depends on whether you're staying automatic or going manual. Despite a GT(assuming you're going to go with a v8) having a different computer from the v6, I do believe the computers for 5 speeds and automatics are different as well. Thus meaning if you're doing an engine swap, make sure you get the computer with it.

If you don't know what you're doing, you are REALLY going to dig yourself into a hole, especially with the newer Mustangs. The motors are expensive and it's not like you can find one as easy as a 5.0. If this is your daily driver forget this idea right now, it won't be a weekend job that you'll just figure out in 12 hours over the weekend. If you do have another mode of transportation, read up on your stuff, educate yourself, and make sure you know what you're getting into. If you don't, your car will be off the road for a long, long time.