Just built and added a rotary to my K40. Everything works well once I understood the settings.
It is attached to the Y axis via a rotary switch (switches between Y and rotary).
I actually run my K40 from CNCJS on a PI. I can see when the gcode is loaded that the Y axis is obviously scaled when created by lightburn. I believe this leads to an issue I am having with the rotary speed being too high as when running a test square in line mode, although it is the correct size it runs too quick on the rotary axis. I understand this may not be an issue with rastering.