In the old days when someone wanted to bump the tail end up a bit on a leaf spring vehicle they just changed or made some longer spring shackles.
Since the original spring is a mono-leaf, it is very likely it has sagged … a LOT. It was a common problem on those type springs. The Code 3 thing is probably the load code. There are usually 3-5 different arches on the springs for different option packages. Minimal arch for lightly optioned and more for the fully loaded trucks. It is required to build the correct ride height at the factory.
Mono-leaf springs were used in base Camaros and Novas into the 70’s to help the ride (no inter-leaf friction). They all sagged after a while so many of them got longer spring shackles.
For what its worth, those longer spring shackles can change a mildly understeering car into one with snap oversteer if they are long enough to get the rear spring eye lower than the front one.