Information provided to me by Rupe Atwood, that will be published in his forthcoming tome:
from the Young wholesale catalogs, this reel is the pattern 15a, and was available in 3-1/8", 3-3/8", 3-1/2" (medium-wide) and 4" sizes.
here's a couple that I fish (and these are delightful to fish - the best I own)
3-1/8" Milward Flycraft, and 3-3/8" ummarked
also Todd, if you turn up a '39-40 L&C catalog, I sure would like a scan of any imported fly reels.