Brothers Performance has just what you need. It's called progressive spring kit for 79-01 mustangs. I believe there springs are made by Eibach. I'll try to put a link to page for you. If not they are $219.
http://www.brothersperformance.com/s...g/bbk2510.html
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96 Crystal White Cobra Coupe
4:10 gears, off-road h-pipe, 2 chamber flowmasters, K&N, pulleys, FMS springs, polyurethane bushing, Steeda Caster/Camber plates