Leave the top jaw alone, it looks like theres a slag or something there either on the cock or the top jaw that could be hanging it up, the tumbler can be touched up with stone, just becareful not to change anything, keep things square, just clean up the edges that have been damaged. The link is no good, get a new one, pay attention to how you install, I believe it makes a difference which way it goes. As for the tumbler in that area, your pic isn't very clear so hard to tell if it's damaged, if it looks damaged, get another one.