I have a '92 suspension under my '85 GT. I used Bilstein shocks and Eibach ProKit springs and have been smiling every day since. Make sure you use a quality caster/camber kit (I love my BBK's). You also may want to consider a couple of other options like Steeda X2 ball joints and steering link offsets. I didn't do the latter 2 mods, but the C/C plates, Bilsteins and ProKits are key!! It's a completely different car!
I got my Bilsteins from Chris at Shox.com in San Diego. I called him up, told him what I wanted to do and since I lived in Carlsbad at the time, he even drove them up to my house that night. Now that's customer service! He cut me a 420.00 price for the struts and shocks. The springs were 100.00, used. Shox.com is currently showing 429.00 for Koni reds, 489.00 for Bilsteins and 479.00 for Tokico Illuminas. There's a guy who has a "buy it now" price of 459.00 for the Bilsteins on ebay. Once again, i LOVE the Bilsteins. I put a set on my 2001 Cobra and love them there, too...completely different animal.