They must be long enough to go from the front all the way to the back. Sorry, couldn't help myself. They are approximately 85 3/4" long for the 3600. With that said, don't go out and have wood cut based on that info. You'll need to measure your box to make sure. Remember, if you do it yourself, measure twice, cut once.
Measure from the front of the lip at the bottom of the front bed panel to the back of the "step" in the rear crossmember. Often the front panel is bowed so the center measures longer than at the sides. Allow a small gap at both ends to give room for the wood swelling. On the bottom shelf of the rear step measure BETWEEN the rear bed wood bolt holes, not center to center, to give you the bed wood width for each position.
