Tsk, remember the last discussion :-)

Cast iron is strong in compression - but weak in tension.

Angle grind if possible a horizontal slot in the side higher up, and a
slot in the bottom.
Alternatively scratch the enamel away (pointed cold chisel), then
drill with something like a HSS-G or whatever is good on cast iron.
Hit the bottom so as to create a tension load so the slots can no
propogate into cracks.

Frankly I am not sure a club hammer is the best thing, I think one of
those hexagonal road bars is probably better because it has both small
area, fantastic kinetic energy, long duration impulse rather than
"bounce off". You would need a short one unless you want to
simultaneously do the ceiling at the same time.