What you need to ask them is if it will fit a 1999 or 2000 Mondero. If it will then it should fit your Cougar.
Personally, I would order a rear ST200 strut brace from http://www.batinc.net/main.htm
for $139.50. I think it will give you the handling you want, especially if you add a front strut brace as well.
If you do go with a bigger rear sway bar, you better reinforce the brackets. Every Cougar owner I have talked to that has put on a bigger rear sway bar has had the stock bracket brace break and had to have bigger ones put on.