put a floor jack under the middle rear of the frame, then then back the two rear sub frame bolts out about 2 inches, the lower the jac to the bolts, leaving the weight on the jack.

when done, just jack the frame back up and make the bolts tight.

oh, and you need the car on jack stands under the rockers if they are not rotted out. i put the jack under the middle of the front part of the frame, then jack it up as high as it will go, then put the j/s under the car.