Deparment of the Army Technical Manual.  Operator's Organizational, Direct support and General Support Maintenance Manual for Generator Set: Gasoline Engine Driven, 4.2KW, 150 Amp, 28V, DC.
Model DC 4.2-Ord /28 (6115-00-857-1397). This manual is dated June 20, 1980.  This manual will ship free via USPS media mail, only to the lower 48 states.