Yes it is the emergency brake lever, it is missing the small pedal pad mount and some other hardware. Here is a picture of everything.
https://www.flickr.com/photos/advance-design_parts_co/8129470811/in/set-72157631868452754
Here is a diagram of how it fits together.
http://chevy.oldcarmanualproject.com/shop/1948_51truck/51ctsm0506.htm