http://www.eternalthroneofdavid.com/jsjb.zip offers this book in html form. They say, "We offered the free on-line book Judah's Sceptre/Joseph's Birthright by J. H. Allen that we compared to as the "Bible" of the Lost Tribes teaching. Now, since the KJV Bible is public domain (free of copyright restrictions like Allen's book)...."
It is in chunks by chapter, it appears, but it seems to be the original without any additions.
Judging from the various web entries, this appears to be the series of beliefs mentioned in No Highway by Nevil Shute....Now if only Shute were available in Sony Reader form, even with DRM. Sigh.