Maybe I'm dense, but I can't seem to get the knob on the source selector to seat fully and it sticks up higher than the others, and has an 1/8" gap between it and the chassis. is this normal for this kit?
Yeah, I looked at it a bit more and the problem is that the rotary switch has a different base that doesn't allow the knob to go down to the chassis. I guess it is what it is ¯\_(ツ)_/¯
2. Cut off all plastic above the mounting nut. Making it flush with the nut is perfect. I used a hacksaw blade (bare blade removed from saw) and took my time being careful not to cut into the shaft as I worked around it.
The trick is getting rid of the plastic above the nut or the knob will never mount flush. Going to a different style of knob could work as well but the BH supplied ones will not mount flush without modification.
When we put out the attenuator upgrade, you may find that you wish you had the extra plastic on the selector switch back (and the attenuator switches have longer shafts as well).