The slant hole is for the ground wire and this will connect to a suitable ground point in the control cavity. Some form of grounding will need to be maintained.
One thing I don’t really understand is that if the original bridge position is correct, as designed (and I think it is) then unless the design is fundamentally wrong, why move it?
If I was trying to establish the correct position I would measure the distance from the front face of the nut to the centre of the twelfth fret. Then, move the bridge saddle of the G string to within a couple of millimetres of its furthest forward position. The break point of the G string saddle should then be positioned at the same distance from the centre of the twelfth fret as the distance from the nut.