First your initial questions: the jumping to the start of the path. When a Simple constraint is initiated the parameters at start and end keyframe are set to 0 and 1 (or vice versa depending on the direction of the path). This brings each object at the start (the seam) of the curve regardless its initial position. The position on the path can be altered by adjusting the value of the parameters as I did in "conveyor chain 001.3dm"
The mathematics are simple: since there are 80 objects on your path the offset is 1 div 80 or 0.0125. Because the curve path is “closed” a parameter values higher than 1 (e.g 1.0125) will push the object past the seam. It is indeed inevitable to set the parameters of each individual object separately.
In the model above I used the ‘To path’ simple constraint because indeed (as you noticed) a “Look Along Curve Normal” doesn’t give any control over the 2 non-constraint directions which makes objects twirl in space unwanted an uncontrollable. The “Look Along Z Up” constraint will make the objects pointing upwards whenever possible. In your model this is useless at the bottom side of the track.
The IK option Marika suggested would be valid when you didn’t have so many objects. In "conveyor chain 002.3dm" I made a chain of 10 clasps in accordance with to the roler-coaster model (http://download.mcneel.com/s3/mcneel/bongo/2.0/samples/en/BongoIK_03.3dm). Theoretically it should work for the whole chain of 80 links but practically you’ll see that when you add more links the IK solver cannot cope with a vast number of linked constraints. This leads to chaos and even apparent ‘hanging’ of the system. So I’m afraid IK isn’t an option either.
In the Train composition animation topic Micha proudly presents his trick using Rhino’s History and Flow command. This technique is set forth in the tutorial-video http://bongo.rhino3d.com/video/the-power-of-history at minute 6. In "conveyor chain 003.3dm" you can see what it would look like for your model. You must press and hold the left/right arrow on the timelineslider to get a Preview of History based animation.
This technique may suffice depending on what the goal of your quest is. In the hidden world of your model I can see that the platforms are driven by a genuine chain with 160 links. Making this work, I feel, would be very very hard. This model is not ideal for starting to learn Bongo!
conveyor chain 000.rar (14.2 MB)