Step 2
Place a large truck with solid bumpers in front of it.

Step 3
Take a Dodge Ram 2500 Pick-up (only thing a dodge is good for) and drive it into the back of the Mustang at 45 Mph.

Result
This will guarantee that your chassis will be 4 - 24 inches shorter than when you started. Now you can impress all your friends with your new custom Mustang. (girls think it is cute!)

Warning!!!!!!
May cause a very slight buckling of rear quarter panels, floor boards, door jams, roof, hood and hatch.