I understand the Magnas are currently on a Model 17 but assume the stocks do not number to the gun.
As scha suggests, they could originally have been on a similar circa 1960 K target gun . . . like the Model 17 . . . but they could also have been on a circa 1957 Model 10 M&P with s/n C387516. Both would have had the diamond around the screw escutcheon but it's likely C387516 Model 10 would have had "modified" (or PC) magnas . . . the kind with the rounded bottom edge.
Here is a picture comparing the two . . . the target style magnas on the left and the modified magnas on the right.
After circa 1952 either style stock could be ordered on any K-frame but which style stock you have likely tells whether it was a circa 1960 K-prefix target or a circa 1957 C-prefix service.
Russ