The DSO is 560307. There is one in the VIN Project (also unknown agency) three VINs later with the same DSO.
http://www.specialservicemustang.net...info176782.htm
There is 86 total in that batch of VINs. There's another one 31 VINs later in that batch with DSO 56030_ (also unknown agency).
http://www.specialservicemustang.net...info176813.htm