interesting weapon, atlatl have stone weights that can be moved to adjust the throw to the dart (spear), and sometimes finger loops, the spear bends as force is applied to the spear end, depending on the length to diameter ratio of the spear and there is a point where the counterbalance weight tunes out some of the vibration, increasing distance and accuracy. a modern atlatl threw a spear 'dart' almost 800 yards, so they are not something to be trifled with. atlatl usually have a 'hook' pivot that engages a cone shaped depression in the end of the 5-7 ft. long dart. no./central/so. american style darts are normally fletched.
i'd imaging a forked 'knock' on the end similar to a big arrow would work for yours, the atlatl sites show very similar throwers to yours.
here's a video showing how they are used.
http://www.arthurhaines.com/primitiv...onstration.wmv
more links for anyone who might want to practice this most ancient art. a very easy to make weapons system....
http://www.thunderbirdatlatl.com/?page_id=78