Some more steps ahead...:
In the following pictures you can see the levers and mechanic system to lift up the rear end of the skid plate at the starting line. After about 3 ft distance the weight box lets the levers move up and the complete sled plate touches the ground.
The original sleds do it the same way. Lifting the rear end of the sled palte up makes it easier to accelerate the "vehicle" at the starting line. At this moment there is almost rolling friction, later when the plate is pushed down it becomes sliding friction.
In the middle of the weight box you see a thick brass bush. It contains the locking pin for the chain...The pin drops into the free space of the chain link.