I did indeed left weight distribution and shocks out as those make thing quite complicated
I think that rear springs are softer than front, but as they are leaf springs they do feel stiffer on bumps as they don't react as well as coil springs.
-0,2 degrees is from factory specs, it really has not much camber at front to make it understeer and safe (That is unsafe from my opinion).
In race use they use 2-3 degrees of camber with 60mm lowered suspension and lot stiffer springs.
Front springs are rated approx 33,6kN/m and I believe they use something near 50kN/m on racing (V360Cup, Holland).
I have no data from rear springs, but only estimate that they are 28-30kN/m but I would need to find this data from somewhere, just is next to impossible to find this, same as damper ratios.
Stiffer springs are not more grip, but actually less, spring rate is usually compromise between grip and handling, if you could make car not to roll and still use very soft springs you would have much more grip around corners, but that is absolutely impossible to make
Spring rates at near 2,2 Hertz are considered good for racing, just I'm missing magic formula to calculate spring rate.
It can be checked when springs are installed to car and when there is no dampers, you push car down and check the rate at which it bounces. Not too high tech method but can help to determine if it is far off from that.
Well, suspension is science of its own, with our cars and possibilites there is not much we can do with science, just need to try find at least some part that will fit.
If you could find 360 leafs from wrecker that would be easiest, but I guess there is not too many of these at down there? Then other cars are typically so big that creates a problem I believe.