They adjustable bars are not so you can change them with increased lift.
"Adaptable" is a better word for them. It gives you room to slide the upper mount on the frame rail if something is in the way....also makes installation a little easier.
The $555 is for the 64" bars with a weld on axle mount, small gusset.
If you lift bigger in the future you can simply purchase the inner/upper tube if need be with the adaptable bars
Small changes in height aren't really an issue with either bar in terms of needing to change the bar or move the mount. Bigger changes in height will need to either get the new tube or move the frame mount.