We have removed the gas fire and chairback etc from the chimney breast and are left with a recess that varies from 61.5 to 62 cm wide. It is lined with concrete blocks. How can I shave the necessary 0.5 cm to get an alcove that is 62 cm wide ( or a tiny bit more) - the inset woodburner we're looking to get fitted needs a 62 cm opening. Scutch chisel in an SDS drill? Conventional spade chisel in an SDS drill? House is late 80s built with concrete block inner wall and brick outer skin.