thats what i thought,
the springs are for a GC8 also, the suspension sat just fine on his gf's GC
here is a pic of that
even seems to be sitting a little higher in the back if anything on the coupe
it is very weird that it would do this.
same thing happened to my other friend's GC when we put legacy suspension on it for winter. jacked the front up but the back stayed at correct height.