Is there less vibration with a 180 degree crank shaft

I have an 81 KZ305 and am amazed how smooth it rides. At all speeds it has much less vibration than any other parallel twin I have ridden. Is this due to the 180 crank?
I'm eyeing a 77 KZ400, But wonder if I will be disappointed with the vibration?

The Kz400 will probably be smoother.  It's what it's known for.  Not because of the 360 crank, but because of the dual balancer shafts.  The Kz400 is much smoother than the ubiquitous Honda Cb350, which uses a 180 crank.  I've never ridden a 305 for comparison, though.

180 or 360, the engine will shake unless it's got balancer shafts.  

Does the 305 have a primary chain?  can't find it in the diagrams. wondering if lacking that would contribute to its smoothness. ???