This is the formula I used to get the basics for for I wanted....in hindsight it is a bit too stiff, on the highway the springrate is great, car does NOT float, corners reallly well, but where potholes are concerned its a bit harsh. My thinking now that it's been 2 years since I installed it the springrate could be dropped to perhaps 280lbs per inch. The shop owner who fabbed this up did it from the original *high arc* leaf. He used regular *shallow* arc leaves (blank leaves are all arced to a basic curve) to start with, cut them to the length as per the formula, then put each one thru the *hammer* to together match what the ride height the car is at when the glas leaf was in place with the cars weight on it. Of course I had him reduce the arc as the car sits approx 1.7" lower.
That means you have to get under the car to measure the curve of the glas leaf when it is under the vehicle weight. Do so from the ends of the leaf to the centre section. I just used a long straight edge, laid it up under the spring ends & took a measurement in the centre. Since I was doing all the *bull work* I had to install, test the ride height, uninstall, go back a couple of times to have him *fine tune* the arc to get all where I wanted it.
One has to fab up their own rubber bushings for this.......not hard to do, just takes time cutting them to fit.
*Note* to do this the exhaust has to be out of the way.