Era Fortress BS Old
Drill to pick:
Measure 21mm up from the top of the keyway then 13mm towards bolt.
Use a 6mm hard-plate drill bit followed by a flat ended drill bit to completely open up the hole without damaging the levers.
Drill for the stump (the last resort):
Measure 20mm up from the top of the keyway then 18mm towards bolt. Consecutive holes may need to be drilled to remove the stump. Use a 6mm hard-plate drill bit.