You bought the best of the 23's (23AA) and in excellent condition. Production date would be around 1937.
The magazine pictured with the "S" is a reproduction (reported to be made on the original tooling). The longer 5 rd. mag is from the 60's(?) and was used in another model that reguired a slightly longer magazine. Both should work fine.
Since your rifle has been D&T'ed (front holes are not factory) and you have the base (lucked out!)I would mount a good 1" rimfire scope (Weaver R2.5-7x28, etc.) on it and go shooting!
