Why cant this be done from the inside? The old fashioned way is with a heavy hammer and masonry chisel. Less dust than gas brick saw. Yea, if I was using one of those I too would do it from outside. For one window I would drill first around the perimeter and then pound away, all from inside. Don't forget the lintel.
If you do it this way you will have Popeye arms when you are done.
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