I have just opened up a late 1930's brick fireplace and need to remove the sooty build-up and remaining plaster/cement from brick surface. How do I do this without scratching or damaging the brick surface as this will be visible when I install a wood burning stove?

Try powerwashing the bricks. The pressure should remove the sediment from the bricks without doing too much to the brick itself... that's the only thing I can really think of...