Zach,
I have the Mathewson/Bridwell and the Evers/Chance and both have the Factory 649 1st District back. They are both in PSA slabs, which, unfortunately are preventing me from getting a clear enough scan to post.
Thank you for a well written article.
Best Regards,
Craig
Edited to add that here is a Mathewson/Bridwell on ebay with the 649 back:
http://cgi.ebay.com/T201-MECCA-DOUBL...#ht_2349wt_732