Very hard to see, I didn't see an "A," but maybe this will help. The piece goes with the tube extending toward the front of the car and the tube angled down. The base, which is roughly shaped like a triangle, has 2 holes in it (I assume but I cannot see the second one). When installed, these holes will be on the top edge of the triangle. There is a weld between the tube and the base on the engine side of the piece when it is installed properly.
You do not need to remove this piece to replace the clutch cable. I found it useful to fabricate a little shepherd's hook out of a clothes hanger to manipulate the cable housing into the tube that guides the cable through the firewall. I find it easiest to get the new cable housing into this tube as the first step in putting the cable in since the housing has to be bent to line up with the tube.