matt why dont you pour a 225mm floorr with a couple of layers of a393 mesh with upright starter bars out of the slab ,then cast a wall at your neighbours and at the back of your garage to act as a retainer wall ,this will do away with the need for a 1100mm footing .concrete walls are a lot stronger than any block wall you put up.just remember to use a water bar at the junction of the wall and floor