needs a little help shocks and springs

my 72 demon has air shocks in the rear and im thinking of removing them for adjustable ones.. my question is how do i know if my springs are good or worn out. when i removed the air from the shocks the rear drops lower then the front. my understanding is that if i take the air out the springs should hold the car at the stock ride height and not sag below the front unless they are weak springs.. is this corrent or is the air shocks pulling the rear down cause i removed the air creating a suction inside the shock? front of car is at the proper ride height from when we did the alignment