My FSM for Gen 2 only covers ABS, but the Gen 1 FSM says that, with the fuel tank full and the truck empty of load, the spring should measure 3.9" (99mm) from the top of the top "hook" to the bottom of the lower hook.
To adjust, you slacken the spring anchor bolt on the arm attached to the suspension, move the bolt and tighten up. I guess if there's not enough adjustment, that's where the blue bracket comes in?
The only thing is that the Gen 2 suspension is different, so the spring force and/or the adjustment value may be different.
Maybe someone with no lift and without ABS could measure his?