I found this on the web about Alco records. These sources might have info the NdeM engines:
"Most of the general files, technical manuals and ALCO designs are located in George Arent Research Library at Syracuse Univerity (Phone: 315-443-2697). The Buider's Photos and many of the Erecting Cards (photographs of the drawings) and
"Painting Diagrams are in the possession of a sub-chapter of the Mohawk & Hudson Chapter of the NRHS. This group of volunteers is known as "ALCO Historic Photos" and is preserving over 32,000 ALCO negatives.
ALCO Historic Photos
P. O. Box 655
Schnectady, NY 12301-0655"