My daughter owns an Olympus OM1 and the Contax 139 was about the same size. A little thicker maybe but not quite as long and much more ergonomic. Of course I am going by memory here.
You're memory is good as I just checked the specs on the 139 compared to the OM1 and MX and they are very similar to within a couple of millimeters. Thanks for the heads up as I was not aware it was that close.