Here is something unusual. a two into one exhaust for a Suzuki T500. If I remember the story correctly it was a one off, custom made for the owner by Gary Wolf who made 4-1 pipes in Ontario in the seventies and eighties.
There were a number of manufacturers who made 3 into 1 pipes for the two stroke triples back in the day. Though they were styled to look like an expansion chamber, it's doubtful they were at all effective or efficient with all the confused soundwaves bouncing around inside them. I expect the same would be true for this setup, though considering the 180° power pulses, only one exhaust port would be open at a time... hmmm. Now where is Gordon Jennings' Two stroke Tuners handbook?