I think they were broken off due to the fact they are fairly thin and stick out a ways from their frame attachment. Here is one from my 50' 3600 which was in place on on a 54' vintage frame I purchased.
http://www.flickr.com/photos/advance-design_parts_co/8129068639/in/set-72157631867396207
This one is from a 47' 3600 which I recently purchased for parts.
http://www.flickr.com/photos/advance-design_parts_co/9152256485/in/set-72157631868452754