I did a full rear subframe, with a drag race specific 4 link (2x3 tube subframe) in a Maverick, and the car lost 133 lbs of weight. A lot of it was from the stock floor removal...and heavy leaf spring removal. I have also done a '69 Chevelle original big block car, that one went from the stock rear suspension and a well built 12 bolt to a 4 link, 15x33's on decent wheels (not lightweight stuff here), and a 9" with discs and that car lost 218 lbs total. I would have thought it'd have been a lot less than that being that the 9" is a little heavy.
Later on I also put an aluminum center section and aluminum spool, and Aerospace brakes on the rear of mine and there went another 87 lbs.
You can make a fox body really light if you plan it correctly. My 347" '85 coupe is right around 2490 + driver (who is about 160), and it's stock 4 cylinder brakes on front and Metric discs on rear. Aerospace on all 4's plus the aluminum chunk in the rear should be worth close to 130 lbs alone. The car is not really worth putting that kind of money into, however. And that is using the stock style triangulated 4 link.
I think a lot of people forget about the importance of weight reduction. Years ago I remember a Hot Rod article where they took a car and started taking parts off and out of it and logging the weight reduction and ET improvement. A bone stock engine and transmission mind you. I seem to remember they got the turd into the 12's down the 1/4 mile just by removing weight, but it was not pretty.
The class you plan on running may have a bearing on your decision too. Some classes require a stock style rear suspension, and if that's the case, a traditional parallel 4 link is out the window. But they flat work and are, IMO, the best option if you don't have the rules stating that you can't run that setup. We're talking full tub, big tires (if you want) and everything. Which reminds me. A certain local class that they called "10.5 outlaw", it's rules stated the tires had to be 10.5" and that the rear suspension had to stay the same design as it originally came with. Well fox body cars came with 4 links. So guys were gutting the whole rear and putting in a full drag-race style 4 link, with 31x10.5W's. It flew with the rules. The original was a 4 link too, although triangulated and not parallel. Didn't matter, it was within the rules. Those guys were running mid 4's back in the day before turbo's got popular, and now most of 'em are turbocharged and can't get down the track due to entirely too much power for the surface. I acutally won the class once with a 5.66 in my rust bucket that might've made 800 hp. My competitor was well north of 2000hp but couldn't get it down the track. 'Course it helped that I treed him big time