See those pivot pins? On the back side, is a washer. It must be bent to release and slide over the end of the pin. That will let you remove the shoes. This is what the "washer" lock looks like:
http://www.classicparts.com/1947-52-Huck-Brake-Anchor-Pin-Lock-Clip/productinfo/71-514/#.VhflW3pViko
Huck brakes are different. They do not pivot at one end, they are more evenly pushed into contact with the drum. That is what those pivot pins do. Take a look at fig.2 from the manual(yes this is the 3/4 ton system): http://chevy.oldcarmanualproject.com/shop/1948_51truck/51ctsm0503.htm
I hope this is helpful.

Steve H