Hello,
I just bought a 403A with table and I love it. I found the Year of Manufacturing on:
http://www.singersewinginfo.co.uk/anderson/
The 403 and 403 are made at different plants. The A in 403A is from the Anderson plant.
Enjoy the machine.
BTW, I'm a 67 year old male and am just starting to sew. My older brother sewed for years at Commercial Sewing in Torrington, CT and now he works at his own shop sewing and making Bimini Tops. Boat covers, Seat covers. He gave me Sears 158.17520 workhorse and it's good but noISY. i LOVE THE 403a
Oh BTW. the serial number is located on the bottom just under the edge of the big lip on the left side. Mine is NA 932370 made in 1958. so it's 60 years old, runs like new.