Interesting! The serial does suggest a late '38 to early '39 date. I've never seen a 3-gill frame with the straight downtube like that. I googled it though and found an old thread from RRB with one of Phil's wonderful CWC responses:
"The frame you have is what could be considered the second series 3-Gill frame. The 3-Gill frame, so called by collectors for the tank that fits it, was one of CWC’s longest running offerings.
The first 3-Gills were introduced in 1938 and the last were produced in the mid fifties. Second series frames are categorized by the upswept chainstays in combination with a straight downtube. By the CWC catalogs this pattern was current and offered only in 1939 and 1940 but it was probably in production before the end of 1938 and may have continued in production until the cessation of bicycle production in early 1942."
