Get longer than stock shocks, or ones that will extend more as so you'll know they won't be binding up the springs/rear.
side note ...I notice someone sags by dropping the rear of the car [raised shackle plates] to help with faster transfer or just a mistake...or something stumbled upon unknowingly , like you know who runnin 11's, his shackles were bound up against the frame when I saw that car last year at the mats..maybe forcing the spring to buckle more/stiffing them.
Made me wonder if that was hindering or helping or specific to the flogged out springs....
The snubber may help you if the front segment of the springs are weak.
Raise the timing till the mph stops increasing, then go back to the last setting that showed an increase.