6491 was built in September 1969, #35478, FN 7194-2, as St Louis-San Francisco 930.  It became Burlington Northern  6678, Class SD-45, in December 1980 and sold to Soo as 6491 in March 1987.  It was retired in June 1992,  It was sold to Morrison-Knudsen Corp as 9528 in March 1993 and sold to Wisconsin Central Ltd as 9528 in 1997.  It was renumbered 6638 and then rebuilt as 7638.

6492 was built in February 1967, #33021, FN 7970-4, as SL-SF 910.  It became BN 6659, Class SD-45, in December 1980 and was retired on September 30, 1986.  It was sold to Soo as 6492 in March 1987 and retired in June 1992.  It was sold to Chrome Locomotive in March 1993 and sold to Morrison Knudsen.  It was rebuilt as Southern Pacific 8586 on May 27, 1994.  It was assigned as Union Pacific 2662, but never repainted.