Steve,
Yesterday I coincidentally followed a thread which posted photos from a book on NC long rifles that used the "Bird" style side plate. Sorry, I can't remember the thread.... But one example was a Thaddeus Gardner gun, of the Jamestown School, and a simpler styled gun built by Robert Polk of the Early Deep River School. The photos were listed as #58 and #50 respectively. Then this AM I found 2 more examples, slightly less stylized, of "your" plate, in this site's archives. I looked under NC, and there is one gun by Thaddeus Gardner (Topic=5545.0, and one under the heading of "William Lamb and Son". (Topic=23024.0) But that gun is apparently miss-labeled, as it is signed "TG & WL. William Lamb was Thaddeus Gardner's nephew and apprentice, and they continued to work together for a time. Sorry I am so limited in sending links... but I thought you would be interested in seeing historical examples of the "bird" plate that MS lists as "contemporary" in their online catalogue.