Darren,
How about just leaving the old stuff in place and stringing new cables beside it, sort of building the new cable structure around the old...then either just leaving the old there, or taking it down in pieces. You could use a torch to cut the old stuff away in pieces sized so you could manage them...
By doing it this way you could work off the old bridge, perhaps somewhat safely...
Just an out-of-the-box thought... /forums/images/graemlins/smile.gif
Don't know if it is a practical idea or not...but I would consider doing it that way if I were doing it myself. Of course if I were standing next to the bridge I may see a dozen reasons why this would not work... /forums/images/graemlins/tongue.gif