My engine mounts are more than likely original with 170K on them and, although it feels a little like a racecar at idle, the vibration is never bothersome or concerning. Most likely balance shafts. Even Porsche shops get it wrong sometimes. I've somehow managed to not screw it up yet, so I don't know what it should feel like when they're off.
Here's what they mean. Make sure both keys face up (which I believe they tend to settle in that position anyway), then install each sprocket in the slot that makes the respective alignment marks line up. The U on the sprockets are no longer present.