There is a great article related to this subject titled "
Air Brake Instructor Ainsworth and the D&RG's Narrow Gauge Changeover to Automatic Air Brakes and Couplers" by Stan Rhine that was recently published in the Rio Grande Modeling and Historical Society Publication “Prospector”.
It is a very good read and highly recommend it. If not already a member of the Rio Grande Modeling and Historical Society (drgw.org), I recommend that as well!
Mike Ramsey