Case and Bezel 10K Gold Filled, Measures 43.30mm lug to lug and 25.10mm not including the crown.
Gang
What's the difference between the Oxford and the Montgomery (at least by case, jewel count, case date, if not dials).
Here's a 1938 ad for the Oxford. Click for full ad in Plains 1938 Oxford record.
I think your right. The date of the two Montgomery ads Dennis used above are both 1939.
Fifth has a Montgomery here, listed as 1939 based on the 1939 (Shield) movement date, although the case serial number begins with 8. It's dated correctly, as we are using the more recent of the two dates when we assume the movement is probably original to the case. However, Fifth does give dimensions for his 1938 case as "43mm lug to lug x 24.5mm using Calipers." Those are very close to the dimensions Dennis gives for subject watch-Measures 43.30mm lug to lug and 25.10mm not including the crown.