The axle is not solid mounted to the spring I have a set of leaf spring Sliders that also free float on the axle housing. The rear of the spring has a slider as well instead of a shackle. So when the axle moves up the pin on the leaf spring can slide back and forth allowing the axle to swing in the ark of the ladder bars and allowing the leaf spring to grow to the rear of the truck
https://www.speedwaymotors.com/Competition-Engineering-C2030-Floating-Housing-Mounts,297048.html?utm_medium=CSEGoogle&utm_source=CSE&utm_campaign=CSEGOOGLE&gclid=CjwKCAjwm4ukBhAuEiwA0zQxk5oBU-n5RaThj6YDxZH_nabrczzCww-WTF9Dqi3YTg0mxrCdWMrKIxoCt0IQAvD_BwE