Sometimes peeps do not notice a slight wheel balance issue which can be exaggerated whilst braking through a specific speed.
However, if it is not something silly then I would be leaning towards DTV.
If you ran the car with the inner face of the wheels powder coated and only returned to get the PC removed after the vibration started then I would guess that it is too late.
You can try another serious bed in process, but you may have to get the discs resurfaced professionally and all other surfaces cleaned up.
Give Marcus a shout at: http://www.discskimmers.com/index.html