My weathering is also acrylic washes and AIM powders. I used powders for the black weathering, and acrylic white washes for some paint fading. I used acrylic paints for the dark stains around the SOO lettering and side sills. I used the Pelle Soerberg spray mix on the fuel tank and trucks (dark skin tone modelmaster paint diluted in water). My white SOO SD60 came out nowhere near as good as your Sd40-2, that white is a pain to weather, did you have any trouble with it?
my best,
Jan