I found an outstanding collection
of Jack Daniel's whiskeys and paraphenalia on the web. The site is run by Jean-Paul Schuurbiers of The Netherlands and both his collection and the page is awesome.
He has a bottle of JD from 1947, which would be right in that area I'm interested in knowing more about. The bottle is round, not square, but JP indicates that was unusual then, too. The label appears to be very similar to the classic black label, except that the words "Sour Mash" are printed much larger. Even larger than "Tennessee".
The other interesting difference is that there's an age statement. In 1947 anyway, Jack Daniel's was 8 years old.