These days buildings are most likely cantilevered from one or more concrete cores rather than steel frame. Rebar is a bit trickier than just plain steel. Also

These days buildings are most likely cantilevered from one or more concrete cores rather than steel frame. Rebar is a bit trickier than just plain steel. Also, the thing is that any type of conversion most likely triggers building code updates rather than being grandfathered in, at which point for a building 50+ years old there’s probably either lead or asbestos.