Be hard to lower a car with a shackle kit. There isn't much room to drop it, any less clearance and you will hit the frame with the spring. Shackle kits ae usually used to raise the rear, another bad idea along with blocks to lower it.

If you want to lower the rear you'd be better off raising the front spring mount up. On many Mopar you can swap the mounts side for side and flip them over to lower the car, you may have to oval the mounting holes a bit.