There are two types of safety skids. On your
1959, with leaf springs, the safety skid can be a piece of metal welded to the bottom of the spring plate to protect the ends of the U-bolts from being ground off. The spring plate itself will keep the wheel off the pavement in case of a flat.
In later single axle models with torsion axles, the skid was a piece of leaf spring, as described above and in the stolen* picture below. These were abandoned because they caused more trouble then they were worth.
*Picture is courtesy macman, who hasn't posted here for several months. "Hey, macman"
http://www.flickr.com/photos/swilson/27650221/