So, I have a spring on both sides of the balls and then sandwich the 2 springs with a center bolt tightened just enough to be secure. The truck in the (previous) picture is the first truck that I made and it has poor articulation so, I don't suggest making it that way. On later trucks I built I didn't attach the springs to the frame I just let the axles float and it has great articulation. I am using the stock suspension components to keep the axle movement correct...the upper "A" shaped arm and the lower links. You could even just use coil springs with this setup if you wanted to.
