After taking apart the locomotives, I weathered these using primarily an airbrush with acrylic paints. After I was done with the airbrush, I came back in and touched up things with weathering chalk.
This is a Kato SD7 Custom weathered Southern Pacific #1442.
This is a Kato SD45 Custom Painted and weathered for St. Louis and San Francisco #925
This is a Atlas GP40-2 Custom Weathered Norfolk Southern #3013
This is a Kato SD45 Custom weathered Chicago and Northwestern #6527