If they don't join right behind the engine, I would expect that they would likely have a merged portion near the resonators, but stay as two pipes the rest of the way.

That being said, I haven't crawled under one to look. The system that I just described was what I found on my euro spec 500 SEC.
The US spec cars that I've looked at had a cross over pipe that came from the left bank to the right, and then down as one single pipe from there.

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-Josh
Testing the cheap Mercedes axiom, one bolt at a time...