I know precisely the book you are looking for...the 3rd grade level includes "Dummy Line" and "Doctor Iron-Beard." They are EXCELLENT....but I know only the 1957-8 versions....and won't sell mine.
The anitique book exchange ABEbooks.com Lists 49 copies of that particular book...I have ordered books from Austrailia and England through their connections....and while the 6 week wait for a book's arrival from "down under" seemed interminal...it was a copy that probably never could have found otherwise.
HAVE FUN and enjoy.