The 6x4 DF-405 was unchanged in appearance from the previous RDF-405. International dropped the “R” designation, possibly to separate the Emeryville-built models from the Fort Wayne-built R-series, but they tended to revert back to the R from time to time. In 1958 Cummins revised some of there engine models. The HRB-600 was increased to 175 hp, the HRFB-600 to 190, and the NHB-600 to 220 hp. Later in the year Cummins combined the smaller 672 ci displacement of the old HB-600 with the 4-valve heads of the NHB-600 to create the 180-hp NH-180, which became the standard engine in all of International’s big-bore diesel trucks. At the same time the 743ci NHB-600 was renamed the NH-220. In mid-1961 the DF-405, with styling that went back to 1950, was replaced by a new DF-405 with a new cab.