They are both pretty much bolt on, but some chose to also weld the front RSK spring hangers to the frame.
The SKY SD kit requires removing & replacing the rear spring perches so a little more work is involved. I think he did this to try to address the positive caster issue caused by the old design.
From what I've read over on PSN, the PMF kit is easier to install.
You can order new springs from a dealer, find them at a local salvage yard, and they are often posted in the classifies on the different truck forums. You'll want U, V, or X code. U's are the softest, X the most firm.
You don't have to replace the rear springs...