I replaced the shocks and springs/upper rubber isolators on my 69's rear end and when you rock the back of the car there is a squeak. We think it may be the bottom of the spring. My question is: Even though the cars didnt come with the isolators on bottom, will it hurt anything if we put them on the bottom also to see it the squeak goes away?

i'm pretty sure the rubber insulator will not fit between the spring and the knob on the bottom spring perch.
top and bottom knobs are different sizes.
you may have a trailing arm bushing squeaking.
get under the car and have someone bounce the car and try and pinpoint the squeak.
david

If the squeak is comming from the lower coil spring, I would use a thin layer of grease around the spring and azle spring perch. That should solve your squeak and it will keep them from rusting!!