you can fit qa1 springs in rear. you will need to just get the correct length. Inside diameter 2.5 inches. i would go with a 12-325 spring rate. Ill see if i can get the part numbe rof the one I did been a few years.
the qa1 springs fit right in thing is you have to make sure to get the correct shock length because if you dont spring will pop out.
Just like on teh trailblazer ss the qa1 fit perfect inside the tahoes.
hit me up ill tell you how to get it right. If you want to go that low you will need to notch the frame but i can help you pick out the correct spring overall length.