If we just think of the difference on the "Heuer" shield below the Autavia scripting, among other notable differences also the 1163T's show a marked difference in the dimension and font. I remember very vividly - as it caught my eye - a picture here, probably posted by Abel, of two side by side where the sizes were a good 15% apart.
Of course if one wants to get a thorough and comprehensive overview of all Siffert generations there was a wonderful post by Paolo on an Italian forum.
Cheers
Fabrizio