Poor dead horse, he's gonna get another beating.... This has been researched by several folks.

There were a few rear spring packs used. Which was used depended ONLY on the body style and options specified on truck.
F250 versus F350 had nothing to do with it. A 250 ordered with the same equipment as a 350 appear to have gotten the exact same springs. Just a thicker block, a different rating on the door tag, and a higher price on the 350.
It is possible more