Thanks for good advice, you both confirm what i was thinking.
I have the car on axle stands front and back with the back ones under the axle, so it has the weight of the car on it now, a bit more weight would straighten the arch on the springs a little bit to make the length a bit longer but they are quite flat at the moment anyway.
i think shorten the prop by 20mm should do it....

Now, to find a machine shop that can do it, and balance it, and on a bank holiday/new year.... mmmmm