Cats, you should be OK anchored onto granite. The next thing to consider would be the elasticity of the walls and frame; but I think you have a good clue in "centuries old", the building has proved itself by now. The only other thing I can think of is the roof slates/tiles - sometimes in old houses they are "hanging" off each other rather than fixed, and might be more easily dislodged; but that can be left for the next time you have a any roof work donw.