Originally Posted by Stretch

Ummm - it is a bit difficult for me to follow exactly what you are up to but I think you might have missed the point that the stiffness or rate of a coil spring is proportional to the number of active coils.

An active coil is a coil that is not touching another.

Look back at the link I gave to that vacuum pump thread to see the equations you need - also please note different springs were fitted with different stiffnesses / rates for different chassis and engine weight combinations. You should ideally pick out a couple of springs that you think you might be able to find and then start from scratch with the measurements and length adjustments.