One comment:
when you cut down a spring you increase its stiffness and when the rebound spring gets compressed the total stiffness (main spring + rebound spring) will be higher and the rebound travel shorter.
If you have a clearance at static ride height for the rebound spring the stiffness is only due to the main spring and is lower.
If there is no clearance, both springs being compressed, the preload doesn't change the stiffness but only the ride height and the point where the rebound spring becomes free.
SSL front suspension kit solves the problem by adjusting the preload of the main spring independently of the rebound spring
which is free at static ride height.
