RFC/RNAS Oxygen Masks

Does anyone have any photographs and/or details of the oxygen masks and equipment introduced in mid-1917 for high flying RFC and RNAS (at the moment I can only find references to it being used on Airco DH4’s) aircraft? I’m looking at making replicas – there’s one well known photograph of an Observer being fitted with one, and a drawing in the Osprey British Air Forces of WW1 (2) book