we have the rear isolator mod as well…
I have the pro kit on my car. The fronts are awesome, the rears sucked ass and they sagged after a few WOT runs lower then the front, and didnt have any give…it was like I didnt even have suspension in the rear…
so I put my stock rear springs in, and removed the rubber top Isolator, and put garden house around the top coil. This is called the “hose mod” for us F-body guys…very popular mod and lowers the car 3/4 " over the stock Isolator…
if you want yours lower, take out the rear isolator and put garden hose around the coil so it wont wear metal on metal.