"I just use a piece of parachute cord with a bowline loop tied in each end for the long string."
Same here. 500# breaking strength is like 5 bucks at places like walmart or lowes or even places like biglots. You want to make it as short as possible without having to actually brace the bow, too long and you will ruin your bow you are tillering. You also want to use the long string as least as possible. Just enough to not have any kinks or hinges. The second it looks braceable brace it on up and go from there.