This is that has been done to make the car lighter:

Stereo (~40 lbs)
No impact on comfort or drivability. The car came to me with an aftermarket stereo that had 2 subs in the rear hatch, 3 amplifiers, and EQ and a CD changer. The first action that I took was to remove all of this. When I placed everything, including all the RCAs, power wires, etc it weighted in at just over 40lbs. This was the most painful and involved process that I have yet to undertake on the Mustang project. The reason for the difficulty was the method by which the old stereo had been installed. The installed had paid little attention to the function of the factory wiring loom and simply tapped into power at the fuse box and added their own loom for the stereo. I had to spend about 2 hour removing the aftermarket stuff, but then spent another 3 hour repairing the factory loom that had been cut in numerous places.

Alarm (~5 lbs)
Depends on how you feel about car alarms and their effectiveness. My next action was to remove the aftermarket car alarm that had been installed in the car. I have been driving cars from the 60’s my entire life and I don’t care much for car alarms, and have learned to operate a manual door lock, so for me this was a no-brainer. The noise maker part of the alarm was probably the heaviest part and in my opinion the least useful, so you could probably just remove that and get most of the weight saving while retaining all of the “useful” alarm functions. All that I need to remove the alarm system was a pair of snips, a screw driver and a crimp connection to repair the ignition kill and door lock circuits that the alarm system tapped into. If you are not comfortable around electronics, I would recommend picking up a wiring diagram for your specific car to make sure you know what each wire does.

Rear Seats (~40lbs)
None but a wee man could fit back there anyhow. All the brackets, seatbelts, fold down covers, hardware and the seats themselves start to add up quickly. The back seat in a Mustang is a joke anyhow.

GT driving lights (~15lbs)
No impact on comfort and drivability. The support for the driving lights on the GT Mustang are not only heavy, but located about as far forward on the car as possible. Mustangs are already nose heavy and do not need additional help. The removal was quick and easy with basic hand tools.

Rear Swaybar(~ 5lbs)
I am not a big fan of rear bars, ask Ryan Hampton, I fought with him about it on the rear of the Formula D Camaro. I feel swaybars are band-aids and do not address the core of handling issues. The rear swaybar on the Fox Mustangs is mounted between the two lower arms of the triangulated 4-link and in my opinion simply serves to make an unsatisfactory rear suspension even worse. I like the feel of the car much more with the swaybar removed, but like the Moose Balls, the bar can be easily re-installed to take it off and see what you think.

Moose Balls (~10lbs)
Supposedly this thing has an impact on NVH, but I could not tell a difference. On the 8.8 rearend Ford has placed a huge cast iron weight that is mounted to the center section with rubber isolators. My research into the part uncovered that it is intended to eliminate certain types of driveline harmonic vibrations, but I was unable to detect any difference with it removed. This was an easy removal and can be re-installed in just a couple of minutes.

Carpet, Jute padding, sills, plastic interior cladding, and extra dashboard and kick panel covers (~25 lbs)
The car is quite a bit louder inside, but I can still talk in the car without having to yell.
At first I removed everything, but the whine of the electric fuel pump was a bit too much for me so I put the heavy jute padding that covers the spare tire area back into the car. The good thing about this piece is that it only takes about 5 seconds to remove at the track so keeping it in the car is not a real weight penalty. I would just make sure that if you do any scaling of the car make sure to remove it as you want you setup optimized to race conditions and not street driving conditions. The car is still a whole lot quieter then my ‘66 Chevelle.

Sun Visors (~2lbs)
They kept falling down and blocking my field of vision. I want to rant a bit here. I have very little love for sun visors, especially those with little vanity mirrors, besides adding weight up high in the car they encourage makeup application whilst driving. They simply must go.

Console (~6lbs)
A car with no place to put cell phones, change, etc. is no fun to drive around town.

Windshield washer fluid bottle.(~2lbs)
It is located mostly underneath fender, but removed easily

HVAC (~75lbs)
This includes all the underdash equipment, hoses, compressor, condenser, drier, etc.