or cardboard with the cams up and the valves down (just like it looks when attached to the block) nothing is going to get bent. The valves are recessed into the head so they won't touch the ground.
The reason for this is that the lifters are not solid. They are filled with oil. If you store them for any amount of time in the wrong orientation (on the side or upside down) the oil will leak out and you will be shelling out 800 clams for new lifters.