I'm going through my pre-1963 Timexes to see if I can figure out when they were made. My Seiko/Timex 400 has a faint inkstamp in the back of
...which doesn't seem to correlate with anything I've seen. Jose's post a few weeks ago on inkstamps doesn't seem to match with this at all, which could indicate that it is 1958, before they started that stamping scheme. Does that sound right?