Thanks Jacques,
Glad to have it behind me quite frankly.
Interesting to note - the spring around the cable that is located in the drum, does not seem to have lost any significant tension.
I also thought I might have taken a bit too much off. One line was at its maximum stretch when I put it back in.
Fortunately when I sat the truck back down on all four tyres, some load came back onto the rear leaves and has provided JUST enough slack. It should improve again when the box is put on the back.