Take out all of your interior, the seats, panels, and carpet. You'll [should] notice black tarry sound deadener under the rear seats, and going upwards on the firewall. The stuff going upwards on the firewall.. cut away as much as you can with an exacto knife [cause I think it helps the heater box seal tight - so dont just go tearing it out like I did
] When you look at the floor you'll notice that from front to back these cars have this weird covering of tarry stuff. You will need a heat gun but if you are extremly persistant [buy a case of beer to help] and a have a scraper [like a drywall scraper or whatevs] use the heat gun and just kinda go behind the heat gun with the scraper under the tar until its all gone, front to back. It's pain staking and you will want to quit half way through, if they used lotsa glue to put it on, but its worth it. Sometimes it comes right off sometimes you chip away bit by bit [i've gutted prolly 10 Stangs so far
] Then peel the insulation from under the carpet - prolly wet or damp anyway. If you remove the rear panels where the seatbelts and speakers are [specially in a hatch] there is rubberized [in the 86 & older ones - newer ones have plastic backing with SHARP staples that are out to get you
] coating sound deadening stuff in there. Basically underneath and behind every panel in the car you will find insulation.
This insulation, along with that funny strips of tar Ford put on the floor in my buddies 86 GT hatch was worth 97 LBs in total. We had him get on a bathroom scale then I would hand him a box and mark the diff... Wont get quite as much out of a Coupe. We were VERY anal about getting every and any bit out that we could though and for some reason his had a ton... wheras my Coupe didn't have as much.
I'm sure everyones mentioned sway bar, dog bone on the rear end, alum driveshaft, front bumper insert - if 4 eyed car you will have to unbolt the brace then cut away the big middle part so you can retain your signal lights...
Funny, I just found the paper from what we got out of my car:
Front sway bar - 22 LBs
Dogbone on rear - 8 LB
Smog pump and hardware - 8 LB
Spare tire and jack etc - 40 LB
Mufflers [Dyno max turbos] - 22 LBs [put straight pipes in cause I have the cats]
Sound deadener and tar:
Bag 1 - 10 LB
Bag 2 - 10 LB
Bag 3 - 32 LB
stock to alum driveshaft - 8 LBs
Rims: from 10 holes with street tires to Weld Draglites w/ street tires and skinnies:
Both rear Welds saved 16 LB
Both frotn skinnies saved 30 LB.
I have Convo Pros now so prolly same.
87 - newer fiberglass Front bumper insert/reinforcement and struts - 24 LBs [have yet to do it to this car but was written on there - I thought it was 27 LBs in another post I started].
Funny I never could find the paper with this stuff written down and today i find it here under some stuff
*edit - noticed you want to keep the sound deadener but figure someone else might get some usage out of my babbling above
Sound deadener after all these years... whenever we've removed it, its always damp and and filled with moisture, and the tar that is glued to the floor - whenever we remove that there's almost always water or condensation under it in the drain channels in the floor pans... sometimes even little holes and rust. i'd ditch it. But you
will get more interior noise - the loudest being the ring and pinion at 45-55 MPH cruise believe it or not. I turn the radio up
The way I see it, the lighter the car is?? The faster it is, better on fuel it is, and easier on brake pads it is.
Cervini hood blows the stocker away in the looks dept though and is a NICE fit, and finished well on the underside. 
