Hi Thad,
This is an interesting website..
Re Sirius and surrounding starfields, I found this:
http://www.obspm.fr/actual/nouvelle/bobi.en.shtml
With the help uf this webpage and knowing Ken's camera scale, the star he thought it was a Pup can be identified, I presume it is the brightest one on the right side of the image.
I also tried to download HST guide star cat for the area withing CdC, but of course, there is almost nothing around Sirius (because of it's glare).
Anyway, this is a very interesting and intriguing problem :-)