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dm65
AgreedI'd be somewhat careful knocking all that out, b all holding up that lintel in the first place, which is then supporting several tons of chimney above, one of the reasons for using a decent builder to do this sort of work
Drill will be used on the plaster/cement sides only. Infill coming out slowly by hand afterwards
Rebuild will be lintel bottom, eng brick with another lintel above the opening for the new fire