Double ended bar
Both power heads turn in the same direction. If you want to see how this works, take two saws, and set them on the floor (garage if married, living room if not) and set them sideways, bar against the floor, as if making a flush cut on a stump. Have both bars pointing in the same direction. You can see how the chains turn in the same direction. Now, take one saw, and rotate it 180 degrees, so it is pointing in the opposite direction (bar still agains the floor). Slide this saw over so its bar is over the other saws bar, and see how the chains move in the same direction, even with the saws turned around. Powerheads on a double ended bar are mounted in this manner.
Now, go into the kitchen and wash some dishes (if married) so you can ask your wife for that double ended bar, or stay in the garage (if not married) and have a beer.
Hope that helps.