[Steve Shauger]

In addition, the same can be said for big block camaros, because both 4leaf and 5 leaf came in those as well. It boiled down to the weight of the car, the ride height and handling package ordered as to what spring rate the car received. A good example of a 4leaf in a BB is Jeff Boone's rs/ss L78 and a 5 leaf is my rs/ssL34. Both survivors and shown in members rides. From a weight perspective mine weighs more based on the fact it has a cast iron intake manifold and deluxe interior. I would speculate that is why mine has the 5 leaf compared to Jeff's cars 4leaf.
If you look in the Chevrolet parts manual you will see a spring chart which is used so that the correct spring is used based on the options(weight of each). I have not reviewed it in years, but I believe it basically like this:

Select suspension rpo car is equipped with first. Then based on the options the car is equipped with and using the weight chart add/subtract weight of each option as it relates to the front and back springs. Finally take the sum of the options (burdened by their weight factor) and select correct spring based on the chart.

BTW, back in the late seveties I tried to buy springs based on the chart from chevy, and basically they gave me a generic(superceded) spring back then, which gave my car incorrect spring height. There is a guy who I have had great success with coilsprings.com he know what he is doing. There is nothing more frustrating than having to repeatedly replace coil spring to get correct ride height ...I know.