The only option that mine didn't come with that I miss from the 03 is the leather seats. I see at a lot of websites that I can buy the OEM seat covers for pretty cheap. Is this something the average person can do in their driveway?
I don't think so. A good upholstery guy will charge about $200 for the install. Still much cheaper than Ford.
Some will tell you that it is dooable. I personally would not attempt it.
It's not bad at all. I know a guy that did just that. Remove the seats and the covers come off in no time according to him. I think they just slip on and there's no stitching or stapling involved. To get the headrests off you'll see a small pin hole on the side of the plastic piece that allows you to raise and lower them. Just stick a pin in the hole and it will allow the headrests to pull off. I'm not sure if the guy had to separate the tops from the bottoms of the seats, but he didn't complain about the job and he's no genious.
The only option that mine didn't come with that I miss from the 03 is the leather seats. I see at a lot of websites that I can buy the OEM seat covers for pretty cheap. Is this something the average person can do in their driveway?
You can certainly do a trim swap yourself in a couple hours. You'd have to remove the seats from the vehicles. The reasons for this are 1) the seat cushion is secured from underneath the seat, and 2) fitting trim properly requires having access to the seat from all sides. You'll need to do a lot of tugging and stuffing to get it looking right. Installing trim on a seat does require some experience to get it right the first time. Once you remove the cloth trim, you may never get the leather to look just right, and if you gave up and tried to reinstall the cloth, it too may never look right. The seats are also run through a hot oven to help tighten the material once the seat is completely assembled. You wont have that luxury. As anthony05gt mentioned, you might have to separate the seat back from the seat cushion (bottom) depending on how the trim is secured.
There's a multitude of fasteners, velcro, etc. that secure the trim to the foam cushion. Also, if you're not careful you could accidentally pull some of these fasteners right from the foam cushion itself since this is where they're secured. Some seat designs call for the trim to be secured to the frame using hog rings (basically a large staple). I'm not sure if this is true for the Mustang, but it is true for the 2009 Ford Flex.
I worked for a tier 1 automotive seating supplier that designed seats for the big three auto manufacturers. Unfortunately we didn't design the Mustang seats so I don't have any specifics for the Mustang, but seating is generally the same throghout the industry. Just some minor differences here and there. If you have anymore questions, please ask.
Interesting information. The guy I know that did his own does definitely have a looser look to the leather than my factory installed leather, but it doesn't look bad at all.