Some of the Rollei mnauals have a cut-away view of the camera including the lenses. For example, page 7 of the 2.8C manual here-
http://www.cameramanuals.org/rolleiflex/rolleiflex_28_c.pdf
Maybe that is still helpful for your camera? A triplet. Telling the front from the back is easy- one has flat back while the other is convex on both sides. I have had problems telling which side goes to the front on the center element. The concaves look very similar. I usually need to run a finger or such across the surfaces to tell which one is the stronger curve. Assemble, test, flip around if it doesn't work.