The spacer is the leveling kit that you bought, most likely. It goes on the spring making it "taller" therefore lifting the front end. The spindle is the piece where your hub, brakes, and control arms mount to. In a lift spindle application, the spindle would be designed with the hub mounting location lower on the new spindle, and would lift the truck. The spindles are more expensive than the spacer, but usually will ride closer to stock because there hasn't been a spring rate change. A spacer can make the spring rate stiffer, and the ride can change accordingly.
