Hello again!
I asked about your machine on the FW board on Yahoo, and I got several responses. Someone who definitely studies the fine details about FWs and their dates of manufacture narrowed the likely dates down to 1940-46. That is based on the type of handwheel (with chrome), the tension assembly (numbered), the placement of the "Singer" decal on the lamp cover, the faceplate and the location of the bobbin tensioner.
Hope that helps!
Ila