For the trunk, I started with the trunk lid, its held on on by four bolts. If your lucky they will com right out. I was not so lucky and had to take a die cutter to two of them and cut off the heads to be able to slide the trunk lid off the hing arms. Remove any liner, or other loose parts in the trunk. There are four bolts holding each of the tail lights in place, remove the bulbs and wiring set the tail light housing aside. At this point the trunk is pretty empty. the main part left is to pull the wiring harness through the side frame rail, and remove it.
My Gas tank has a drain plug on the bottom, so I removed the pipe plug and drained the tank. If there is no pipe plug, then siphon the gas out of the tank. Once the tank is empty remove the tank filler pipe and cap. Then remove all the bolts from around the tank. If the frame around the tank is very rusty, you may have trouble removing the bolts, or you may even break off parts of the body. If so, make a note as new metal will have to be welded in when you start repairing the trunk area.
Once all the bolts and the filler pipe were removed, the tank can come out. Breaking the tank lose is a chore as it was installed with a sealer that goes all around the lip of the tank, this was to keep moisture and dirt out of the trunk. I used a small pry bar and carefully walked it around the tank to break it free. Be careful not to bend the frame or the gas tank lip. If you tank is very rusty, or even looks like it has a leak, order a new tank, they are not expensive and may save you from watching your newly restored Mustang burn to the ground from a gas leak.
Removing the Bumper is simple, remove the four bolts holding it to the car. Once the bumper is off, you can remove the lower valance. There are a lot of screws just behind the bumper that hold lower valance in place. Plus two hidden bolts at the ends of the valance. The bolts can be accessed from inside the trunk as shown in the photo Trunk-3
Removing the rear axel seems simple enough, there are just four bolts holding it in place; however If your car is like mine those bolts are 40 + years old and pretty set in their ways. I used an air impact driver to loosen the bolts and managed to get all but one out with a little heat, WD40 and the impact driver. One of the front bolts had rusted to the inner sleeve of the rubber insulator and would just spin in place. I wound up taking a saws-all and cutting between the spring and the perch on both sides to cut the bolt down to allow the spring the slid through. I left the wheels on the axle and just rolled it out from under the car.
The photo, stripped Body shell, is what my car looks like at this point. Just an empty shell. Note the jack stands on the frame rail, just in case the chassis is weak and it would sag with the doors removed.