To disassemble the mag, take a pencil and push down the follower a few inches and insert the hammer strut through to hold the spring. Shake the mag and let the follower drop out. Put your thumb over top of the mag and pull the hammer strut out to release the spring. Take the spring out, noting the direction it comes out. Clean inside the mag and wipe the spring and follower off too.

Take some detailed photos of that S&W and post them on www.smith-wessonforum.com to find out more about it. Those stocks could be factory...I do not know enough about the older guns to help you.