In 1963 snowmachines (as they were called then) were in their early stages.  There were no groomed trails back then.  This sled had little ski pressure because the motor was in the rear.  Also, a seated riders weight was more to the rear.
 
I don't know if they added the 3/8" square bar stock for added wear or to create more resistance to help turn.  Either way it was a plus-plus improvement.

The design worked fine in deep snow but once it got into the real world of trail riding the wear was focused on the keel bottoms. They ended up welding square stock onto the contact section of the keels.