Another thought I had was to make a shim and place between the mount and frame
...?.... My mounts have bolts
That would make all of the height difference in the world without changing the complex geometry involved with lengthening the shackles. When you just lengthen the shackles by 1 inch, you do not gain 1 inch of lift at all loads due to spring action forcing the shackles rearward, eliminating any of your desired lift.
I would use steel shims between the frame and the mounts.
Carl
