I bought a used set, previous owner said he cut 1/2 coil off. I installed them like that and the car sat a little high. I ran it like that and felt no difference from the 6 cyl springs. I took it apart and cut another 1/2 coil. I honestly can't remember if that was right or if I did it again, but when the car sat right there was a world of difference in how the car worked. It stopped just popping up and dropping back down on launch. It started lifting and staying up.
One thing for sure is use a Snapon,Branick spring compressor. break the A arm at the ball joint and use the spring compressor to collapse the spring as much as possible. I have to use a short piece of pipe on the center screw to keep it from hitting the frame at the top when installing the spring. I pull it down tight with an impact gun. It's not for the faint of heart. You can remove the compressor once the ball joint is attached and drop it out the bottom of the control arm
http://www.ebay.com/itm/COIL-SPRING-...item3f3a71b012
This is the style compressor I use with the fork at the bottom. Be sure it's a name brand piece and not some China junk.