Hi Dave,
I have a 100mm vice on my X3 mill, so maybe a 75mmor 80mm for your X2. The vice did come with a swivel base but I seldom use it. 99% of my work is aligned with the X or Y axis..
I have added keys to the bottom of the vice for quick alignment, which is all that is required for most of my work. Saves heaps of time setting up. For precision work I remove the keys and accurately align the vice or use a screwless type of vice.
Refer to link for key modification. https://www.youtube.com/watch?v=5ISj3Ad4vBU
Paul.