I don't know much about it, alas, except when it was turned in and shelved. The copy at UCLA isn't even complete; the one time I attempted to read it was more confusing than enlightening.
I do know that John D.F. Black filed for arbitration with the WGA for credit on "The Menagerie," claiming he came up with the story of the envelope in this earlier version of it, but he lost the arbitration, giving Roddenberry sole credit. I think that information is from the Solow/Justman book, although it might be from one of the two Roddenberry biographies by Engel or Alexander.
As far as I know, Black is still alive. Perhaps someone here is in contact with him and could shed some light on this script? I'd certainly be happy to hear about it.