Between now and when I can check my chassis manual... there are some great threads in the archives on this stuff... and I think I have taken pictures of those reference pages on this subject...
What MB does... in its overkill on each item... is to make the springs and then measure the wire diameter..... which relates to compression height at a certain number of pounds of pressure applied to them... ( in foreign weights of course )... but does allow you to see the differences in strength due to wire thickness...
Then there are also pages and pages of different rubber cushions which are used to get the cars level side to side...down to things like if a car has one kind of accessory but not another... amazingly anal retentive...
The funny part of this last paragraph is that if a car is that prone to weight then the weight of the driver needs to be taken into account..
I am all for new springs... but if you have a good local shop this might be faster sometimes... if you coordinate with the shop so their ovens are going the day you bring them in... they may can complete it while you have lunch.. and it saves shipping ... and you could specify the height you wanted them.. in case you carry more in your trunk than others... or have a trailer hitch...