After removing 70 years of grime, rust and asbestos dust from the end of the cam I found some tiny letters stamped "outside" and a small arrow. So yes it goes with the long side of the cam to the outside, where it operates the leading shoe.
I guess it makes sense too because the outside lobe of the cam is further from the pivot point of the shoes, so needs to be moved further out in order to get the same angle as the other shoe with the cam lobe closer to the pivot point. But I have never seen this odd cam set up on any other bike I have ever worked on. Weird!