G'day again the first photo looks like my original jib halyard tensioner but would certainly work as your current downhaul.
Whats the 3rd photo attatched to? That will give me the clue of where things end up.
The second photo is your jib halyard the end your showing attatches to the top of the jib. If the third photo is the other end of your jib halyard, that will go from where the rope's tied to the becket down to the block on the base of the mast back up through the block in photo 3 then into the V cleat.
regards