Which leaf springs to use?

There is nothing wrong with the SS springs.
I would probably use the 3400 lb application.

They are WAY heavier than Calvert springs and Calvert
will work with you on the ride height (Adjustable by changing
the rear segments).
John,

Do you know if the rear segments can be made shorter? Long story short, I burned in a set of sliders a touch (.75") too far forward and would rather not cut them off and reweld.... lol