Yeah the vibration difference between the two engines really is a non event, I have a 701 with new engine and 690 with the older engine, there is not much in it from a vibration point of view. I personally prefer the older engine, it has more bottom end grunt.
I put a Leo Vince on mine, it's flippen awesome. Discovered that the cap screw holding the DB killer in was tack welded, but managed to break the weld with the right tools and some force, so it sounds proper.