Thanks everyone. The Frogleggs seem quite forgiving of the type of cable--all you need is a stop at one end (it sticks out in an unsightly manner, but that is life) and cable thick enough that the grub screw on the other end will hold it. Brake cable seems to be working fine.
Sadly, a long straddle cable has not cured the crazy chatter of the steel forks on my Kelly. Back to the drawing board.