Are the XR-7 springs the same spec as the Supercoupe? As far as stiffness goes. I'm looking for a set to upgrade the stockers on my 97. I considered buying Eibach's or Vogtland, but from what I hear the SC springs are a good bit stiffer. If the XR-7 Springs are the same that would be perfect as there are quite a bit more cougars than thunderbirds at the local yard. Thanks!