I also have a Sylvester Wright patent brace/wrench and have sold a couple others. There is an attachment adapter for drill bits shown in the patent but I have only seen one complete.
See the DATAMP entry for a picture of a complete one from MJD auction.
http://www.datamp.org/patents/advance.php?pn=145710&id=5766&set=76 (http://www.datamp.org/patents/advance.php?pn=145710&id=5766&set=76)
(http://www.datamp.org/images/5766-2.jpg)
I have always wondered the purpose of the little tab below the head.
Vern Nail had a brand new one of these Sylevester Wright wrenches for sale in the April 13-15, 2006 auction of his wrench collection.
That was one of my early auctions. Tool was like new but was lacking the bit holder attachment.
(http://myweb.cableone.net/laurammi/nail/0813-817.jpg)