Sorry for the long pause, I have now modified the chassis rails by cutting out a nice curve for the spring
The Spring pulled with a ratchet strap to its flat position
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I marked the rail at the point of greatest travel
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The end result but with the axle having no weight at all on.
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The short drive was great no knocking or any thing else, I did fit all new poly bushes front and back so it should last a while now.
Just need to treat the exposed metal now and it'e ready.
Thanks for all the comments and advice.