Have you considered filling the current hole with something like JB Weld Steel Stik and redrilling at a better angle ? (not sure if the body of the brake boss/bridge will allow you to do this?)
Appreciate this perhaps isn't an area you want to risk something coming unstuck, but should leave minimum JB Weld after drilling, just enough to reset the angle.
Have you considered filling the current hole with something like JB Weld Steel Stik and redrilling at a better angle ? (not sure if the body of the brake boss/bridge will allow you to do this?)
Appreciate this perhaps isn't an area you want to risk something coming unstuck, but should leave minimum JB Weld after drilling, just enough to reset the angle.
https://www.jbweld.co.uk/steelstikep