I went home last night and pulled out the SCSW. In the list of Performance Center production codes and the models they correspond to is the following.
Product code - 170112 4516 7sh 3 1/2 GB DA SS (Pcct)
The 3 1/2 I find interesting. Unless it is a misprint that indicates the PC 4516 had a barrel length 1/4" shorter than the standard production models.
I've no idea what the "GB" and "(Pcct)" mean. Perhaps one of the experts will descend from Mount Springfield and enlighten the great unwashed with a decode and some details on this unicorn.
Regards 18DAI