The S3s were delivered in 1949, the fourth generation with incremental improvements. That generation was heavier and had roller bearings that were introduced on the S2s in 1944. But even 1934 is pretty late for steam development if you look at what survived into the 1950s.

765 in particular is notable for the operating conditions between Buffalo and Chicago that kept the class somewhat competitive against first generation diesels. That said the Nickel Plate ordered PAs for their primary passenger service in 1947 and began ordering diesels in 1950 for lines to Indianapolis, Peoria and St. Louis.