George, fantastic work! Papipeguy, a pipe to be treasured.
On the dating, I would think WWII 1940's perhaps. For 1936, the expected Patent No. would be 417574 (bear with me here) the note in David Field's article at pipedia where the 1341418/20 is mentioned reads,
For the years 1925-34 other patent numbers were sometimes used in place of 119708/17 & 116989/17. Some examples are: 5861/12 (English); 1341418/20 (U.S.); 1130806/15 (U.S.); 1343253/20 U.S.); 1861910/32 (U.S. - used only for Vernon Dunhill fitment pipe).
Note the years he cites for this,
1925-34.
The alternative 1940's dating theory is covered here by John Loring,
A Hypothetical WWII Pipe,
http://loringpage.com/pipearticles/Hypothetical%20WWII%20Pipe.htm
Also note in Loring's article the discussion of horn stems, and their fragility.
This later dating is based on these published materials (I'm no wizard, that's George's job!).
The 1 in 137/1 refers to, from what I have read, the size of the inner tube.