Henry, it all depends on what YOU want. Most Squarebird aftermarket rear springs have 5 leafs. Some vendors sell sets with 6 leafs. I have never heard of seven. Pardon me for saying but, the ride must be stiff as a truck.
We have plenty of pictures showing 'stance' of the Thunderbirds as they left the factory. We also have measurements. How you prefer your car to be, is personal choice.
BTW, I know measurements are commonly done from the center of the wheel to the bottom lip. With new tire and wheel profiles, it's my belief that measuring from the GROUND to the lip is a more accurate method. - Dave