The Stovebolt Site Forums The Shop Area Paint and Body Shop 1966 k20 cab supports

I'm looking at a truck with a fair amount of rust and one of the places that concerns me the most is what i would call the rear cab support c-beam. it looks like it attaches at the cab mount bracket thingy and runs down to the edge of the cab kinda near the rear of the door. is this a big problem? almnost every single one i have looked at is like this. also, what is this called so i can look it up at jim carters website to try and replace it?

thanks