This site claims to have brake shoes for the 55 3/4 ton. Do these look right?

http://www.rockauto.com/catalog/x,carcode,1326372,parttype,1688

And these folks have some as well as the kits.

http://www.lmctruck.com/icatalog/ca/full.aspx?Page=94

Unless I have missed what you are looking for? Done that plenty of times.

Steve H