The SDL39 was a Milwaukee Road only unit from EMD. They were built to replace Alco RSD and RS units in service on the very lightweight rail on the MILW's many branch lines. These were custom built, 10 total, 9 survived to go to Soo and then Wisconsin Central ownership. After the WC was taken over, the surviving 9 went to South America, I believe.\
The SD10s were the MILW's attempt at a Paducah-style rebuilding program for upgraded six-axle road power, similar to the MILW's GP20 program for four axle units. The SD10s were mostly SD7s and a few SD9s. One SD10 is preserved in an Indiana railroad museum.