Right now Yankee hoggers and brake-heads, engine hostlers, car knockers and gandy dancers are delivering goods in five continents. They are operating rail lines from Alaska to North Africa and from Iran to Caledonia ... This Week Magazine March 11, 1944

One of the most important documents on this blog!

Great list from Wikipedia page for the Military Railway Service units - 1st 2nd and 3rd MRS  
 

List of Railway Grand Divisions and their sponsors
Unit      Sponsor     Date of Activation
701st     New York Central Railroad     01/11/1943
702nd     Union Pacific Railroad     10/15/1942
703rd     Atlantic Coast Line Railroad     08/01/1943
704th     Great Northern Railway     11/30/1942
705th     Southern Pacific Lines     05/19/1943
706th     Pennsylvania Railroad     08/06/1943
707th     Southern Railway     06/10/1943
708th     Baltimore and Ohio Railroad     04/06/1943
709th     Association of American Railroads     03/15/1944
710th     Atchison, Topeka and Santa Fe Railway     12/14/1943
774th     None (Organized in Italy)     1944
 

List of Railway Operating Battalions
Unit     Sponsor     Date of Activation
711th     Training Battalion. Built and maintained the 50 mile Claiborne-Polk Military Railroad     05/01/1941
712th     Reading Railroad     10/25/1942
713th     Atchison, Topeka and Santa Fe Railway     04/15/1942
714th     Chicago, St. Paul, Minneapolis and Omaha Railway     10/31/1942
715th     Illinois Central Railroad     10/31/1942
716th     Southern Pacific Lines     12/21/1943
717th     Pennsylvania Railroad     12/01/1943
718th     Cleveland, Cincinnati, Chicago and St. Louis Railway     12/14/1943
719th     Texas and New Orleans Railroad     09/01/1943
720th     Chicago and North Western Railway     08/26/1943
721st     New York Central Railroad     04/14/1943
722nd     Seaboard Air Line Railroad     12/14/1943
723rd     Union Pacific Railroad     12/28/1943
724th     Pennsylvania Railroad     12/28/1943
725th     Chicago, Rock Island and Pacific Railroad     02/17/1943
726th     Wabash Railroad     06/26/1943
727th     Southern Railway     03/15/1942
728th     Louisville and Nashville Railroad     01/11/1943
729th     New York, New Haven and Hartford Railroad     01/11/1943
730th     Pennsylvania Railroad     05/15/1942
731st     Union Pacific Railroad     Did not Activate
732nd     Great Northern Railway     01/12/1944
733rd     Central of Georgia Railway     11/23/1943
734th     Texas and New Orleans Railroad     02/23/1944
735th     ARR/Erie Railroad     02/10/1944
736th     New York Central     Did not Activate
737th     New York Central     09/30/1944
738th     Chicago Great Western Railway     Did not Activate
739th     Lehigh Valley Railroad     Did not Activate
740th     Chesapeake and Ohio Railway     12/14/1943
741st     Gulf, Mobile and Ohio Railroad     01/12/1944
742nd     Pennsylvania Railroad     Did not Activate
743rd     Illinois Central Railroad     01/12/1944
744th     Chicago, Milwaukee, St. Paul and Pacific Railroad     12/21/1943
745th     Chicago, Burlington and Quincy Railroad     05/19/1943
746th     Missouri–Kansas–Texas Railroad     05/04/1944
747th     Atchison, Topeka and Santa Fe Railway     Did not Activate
748th     Texas and Pacific Railway     05/12/1943
749th     New York, New Haven and Hartford Railroad     02/23/1943
750th     St. Louis – San Francisco Railway     03/21/1944
751st     Denver and Rio Grande Western Railroad     Did not Activate
752nd     Boston and Maine Railroad     05/04/1944
759th     Missouri Pacific Railroad     09/01/1942
761st     Railway Transportation Company     07/22/1942
770th     None     08/09/1942
790th     None     07/08/1943
791st     No sponsorship (activated at Andimeshk, Iran)     07/01/1943
 

List of Railway Shop Battalions
Unit     Sponsor     Date of Activation
753d     Cleveland, Cincinnati, Chicago and St. Louis Railway     04/15/1942
754th     Southern Pacific Lines     10/25/1942
755th     Norfolk & Western Railway     11/30/1942
756th     Pennsylvania Railroad     01/11/1943
757th     Chicago, Milwaukee, St. Paul and Pacific Railroad     06/10/1943
758th     Atchison, Topeka & Santa Fe Railway     04/06/1943
760th     No sponsorship     06/16/1942
762d     No sponsorship     10/15/1942
763d     Delaware, Lackawanna and Western Railroad; Lehigh Valley Railroad     07/27/1943
764th     Boston & Maine Railroad     10/25/1943
765th     Erie Railroad     05/01/1944
766th     Association of American Railroads     07/17/1944

Note: The 760th and 762d were RSB (Diesel); all others were RSB (Steam).

Army Transportation Journal, Vol. 3, No. 5 (SEPTEMBER-OCTOBER, 1947), p. 22,24

PART 1: The Military Railway Service 

PART 2: The Military Railway Service 

 Army Transportation Journal, Vol. 4, No. 4 (JULY/AUGUST, 1948), pp. 16-18, 44-45

National Defense Transportation Journal , MAY-JUNE, 1951, Vol. 7, No. 3 (MAYJUNE, 1951), pp. 31-34