Many thanks Greg for taking the time to write down how your downhaul system works. Sadly my mast has nothing more than two swivel control cleats rivetted to either side of the mast at the base. I use a double block system where one set of blocks is attached to an eyehole in the foot of the main. The second set of blocks is attached to a shackle, attached to a loop of cord tied around the boom fitting on the mast. The two ends of cordage coming from the blocks are fed through the swivel control cleats. It works, but the range of movement of the main is about 10 inches which is probably not enough to depower the main.
Cheers
Chris