....snip.... It's the brake kit, yes. The DoctorDiff 13" cobra style rotor kit adds about 5/16" to the track width, or basically 5mm. I'm not sure if its the hubs or the rotors or where it comes in. Andy's original Viper kit added like an extra 1/2" to the track, but that was before the aluminum hubs that are used now.
I've spoken with Cass about it, the current 13" kits only add 5/16" compared to the track width of the stock 73+ disks (although that track is wider than the SBP cars). I try to always give my offsets relative to the 73+ factory disks.
