Please do not consider using blocks on leaf springs, EVER.
This came about for, well I won't say it, but Forrest Gump has a saying for it. Cheap 4x4 trick from the 70's, works until a blocks twists out and they will, just give it time.
Shackles, H style only.
Leaf springs can be re-arched some what or custom lengths can be had fairly cheap.