Tim,
The length will depend how your going to mount it
I couldn't resist after your title to this thread. Anyway, it does depend on whether you are planning on mounting the handle next to the tunnel or on top of the tunnel. Basically, short on top and longer if on the floor next to the tunnel. I used the Lokar , they have a number of applications for the cables (attaching to different rearends) and the cable can be sized to fit. It comes with the necessary hardware which also aids in installation and I would recommend using their cable kit rather than trying to piece together your cabling.
Hope this helps some,
Mike "monster"