Whenever an officer who has been selected for promotion by a selective board convened under the provisions of the Reserve Officer Personnel Act (Sections 3362 and 8366, Title 10, U. S. Code) is immediately faced with withdrawal of his Federal status as a National Guard officer and transfer to the Army Reserve he may be transferred or assigned to a suitable position vacancy in which he can be promoted, subject to concurrence of commanders concerned and approval of the Adjutant General.