The 200 series freight units ran till about 1982. About that time they purchased the SD24's from Precesion National. They were used in northern Iowa around Oelwein, Marshalltown, Mason Sity, and Albert Lea, MN.
Now in Chicago, the 400 series surburban F7's moonlighted in freight service on the weekends pulling autoracks to Janesville, WI, Belvidere, IL, and pulling manifest freights to Butler, WI. That lasted until about 1983 ahen they were replaced by F40PH's.
At that time a small handfull were choosen to be rebuilt for executive service. When they were power short, they would often be used for "Falcon Service" trains. Mighty big shoes to fill for a 35 year old F-unit.