I also own an older model 60 in ".38 S&W SPL" which I purchased used at a gun show in 1986. The SN is: AEC50XX and it has a few additional markings.
Inside the yoke area of the frame: MOD. 60
On the swing-out portion: 2 X 4 # 9 where the # appears to be some symbol I don't recognize.
Additional markings on the swing out in larger letters stamped sideways: S and then B11
Under the grips on the left side are 4 different groups: B11, 2 x 4 # 9, F15, S
Under the grips on the right side are 3 different groups: A circle with a U in it, a triangle with a V in it, and 7677
Any ideas what all of these markings are?
It is a great gun and I will carry it over my 1911 or Glock 23 on my "light days".
Edmo