Cool project! I think there is a huge misconception when it comes to ride quality and spring rate. Ride quality is more about the balance between the shock and the spring. When they work well together its a real pleasure. I think the tendency to over spring the rear is the most common way to destroy ride quality. The single best thing we do for ride quality is chassis stiffening. When all the stiffening is done from front to back, so many noises disappear you'd be surprised. Our unibodies in stock form are weak compared to newer cars.