I did mine two summers ago. One of the biggest pains I have encountered, really I wish I had not done it myself. Sure the end product turned out alright, little messed up on the back of the seat, but when you look into the car it looks great. My tips for you. Have a hair dryer, use this to stretch out the vinyl seat covers. I did most of my work when it was 85 plus degrees so I just laid my seats in the sun to make them more pliable. Also, read a few articles on how to do this job before hand to learn the different techniques to finish the job. My personal experience lead me to believe that the bottoms were easier to finish than the back of the seats. As a result I would say do the bottom first to get the technique down, then do the back of the seat. Also go and pick up some burlap from a store that sells it such as Michael's, Linens and Things, or any craft store. This is used to place the foam on and is usually pretty messed up. At this point you may also want to check the frame of the seats for any cracks or developing cracks that may cause you to have to drive down the street with a "gangsta lean." If you can borrow a welder, this would be the best time to sure these areas up. Though I didn't have the gangsta lean, after examining the frame I found one or two cracks that would have definitely broken within a few months. Other than that, I don't know what else to tell you but good luck.
I did mine and it was not that big a deal. I would say that you should get the better hog ring pliers. I got the cheap ones and I "did" get what I paid for. Take a real good mental note as to where the old rings come out, this will help when pushing the new rings through a couple of inches of foam. When you start hog ringing, start at the rounded corners and then check for alignment. Then when you start placing rings, alternate sides. This will keep the fabric from looking warped.
The wire that slides into the seat fabric that the rings loop around will most likely be rusted bad. Get new ones! Take it slow and plan on having some sore hands for a couple of days! The hair dryer is a must! The fabric cools quickly, so keep it warmed every minute or so.
Mustangs Monthly has had numerous articles about the job or you can go to any bookstore and purchase a basic upholstery book from the Auto section. When your done, brag about it to all of your friends! Good luck!
The advice that has already been given is great, especially the good hog ring pliers I got the padded grip one's and yes they were worth the extra bucks. I did all mine by myself and I recommend that you have someone to help hold or push down when you are trying to get some of those tough rings on.
This time of year I would try and do it somewhere heated and use the hair dryer, do one seat at a time so if you forget how something goes, you can also add strips of thin foam in spots to bring back the fullness. I used spray adhesive on these strips and after I was ready to install spray some silicone on the foam it helps them slide over the foam without grabing.
I took my time with the frames and cleaned and repainted with POR15, Remember this is time consuming and yes your hands will be sore
The best way is to pay somebody else to do it!!!!!!!! I did mine last year and agree everything above. In addition, I recommend finding the curved hog ring pliers. Be sure to replace the foam seat pads. I elected to add a little addition top padding and not use the top wire. It doesn't look as original, but its much more comfortable, and I've never been "dinged" at MCA sanctioned car shows. Just remember heat and silicone spray are your friends, the hog ring pliers that come with the kits are your enemy.