to me it does look to be a ac or ag.

Take a small amount of oil, at this point in time it doesn't really matter if its sewing machine oil or cooking oil and put it on the stamped number. When you wipe it off the oil will make the letters and numbers stand out better. This will help even if the number/letter is faint.

thanks for getting back to us!

Update, a friend of my DD wants to learn to work on these old machines, so I am going to dig out my sewing machine repair and maintenance textbook I bought a few years ago, and let him learn by doing. I told him, that if he got it up and running, and clean, I would make him the quilt he is always begging for. (He had a "grandma made" as a child that he remembers fondly. It is long gone now, but I told him I would make him a purple replacement.) (At least it is not another blue quilt! I have made four blue quilts in the last two years.)

Madame: A really great solution. Please take pictures of his progress.+

you can print out a manual for that machine also,
http://www.ismacs.net/singer_sewing_...ine-manual.pdf
or buy the real thing on Ebay