They are not cage nuts but a very specific lock plate that is drilled and threaded. They are not reproduced as far as I know send me a PM I can probably help you out here is a picture of them.
http://good-times.webshots.com/photo/2492688590102454676vhyrgA
http://good-times.webshots.com/photo/2432157460102454676VeLKTN
There are two styles 1947-50 which are 1/4" thick and the later 1952-54/55 versions which are about 3/16" thick. They fit in a pocket inside the body, stick your head in behind the door and you can see them. They are serrated to lock tightly into place in the pocket once you have the latch/door aligned.