I just got my 6" BDS springs and the BDS front box kit with them, well my question is that the front springs have shims already on them and then the rear does not, but in the front box kit they gave me it has more shims, are these just extras for the front or are they used for the back springs, the holes in the shims are too small to fit on the rears, do you have to take the center bolt out, cuz if so i would need a longer one where would i get one.