joe,

After you perform the attach to motion path you will have a creation node containing the twist property. With the timeline at frame one, right click on the twist property in the channel box and select "key selected". Then move the time slider to the last frame, and set the value in the twist property to (90 x <the number of frames>) and then right click and select "key selected". Now the link should rotate 90 deg at each frame of the motion path.