My question is; does the wire with the pulley come down to a little above the boom? If so, then it is part of a topping lift for the boom. You would run a line from the boom, through the block and back to a cleat on the boom so that you can drop the main without having the boom fall into the cockpit. This allows you to lift up the boom when you are at anchor, and lower it (with a slack topping lift) when you are sailing. If it goes lower than the boom, the previous owner must have has some form of back stay rigged to the stern of the boat. Connie M15 #400 LEPPO