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The only kit I have experience with is the Rippie kit on my car. It uses stock shock mounting locations, but they valve the shocks (Bilstiens) to the specs you give. Or you tell them what you're using the car for and they valve them to a few different options they have. They then match the spring to the shock and away you go.
The kit for auto-x (which I'm guessing you'd want based on your sig pic) is somewhere around $1000, depending if you have FX-3 or not. Go to http://www.dougrippie.com.
Rob, 1200/600 lb springs??? Lemme guess. California. A recommendation from a certain BSP C4 driver that is a huge, "more spring is better" proponent. I gotta believe that if you don't have a full cage, you're gonna just twist that C4 into a pretzel. If that's the way you want to go, (don't you get bumped to BP or something mod?) you can buy any spring rate you want from any of the circle track suppliers for about $160 for a set of four. Guaranteed to stay within a couple of % of the orignial rate for as long as you run it.
H-rocks is right on the circle track supplier point. Afco, for instance, is one of many suppliers of coilover supplies. All you have to do is figure out the mounting method and you're good. If yu go with the circle trac kboys you can buy 3-4 sets and experiment for the price of one set from Rippey.
For what it's worth, I thought more people were running springs in the 600-700 front rate and 300-400 rear?