Stock is 430-550# variable rate.
I personally ran the Eibach "street" springs which are 10% stiffer 450-580. Great spring.
I got a little more into opentrack racing and went with 650# linear BBK springs.
Now I Finally got the right ones, and got some 800# (400#) coilover springs.
Personally I would go with the Eibach ones that I had.
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Darius Rudis
Roadracer: Home built t-arm/panhard suspension powered by an S-trimmed motor :-)
My Mustang Page