I noticed that the B&M had 6 GP18's, only the last one, 1755, had the two 48inch cooling fans, the first 5 had the four 36 inch cooling fans. That in itself seems it would be easier to model. The Red Caboose unit is a good starting point.
I also saw that OSA or Des Plaines Hobbies offered a low nose, wondered if it had the slope to it.
Good Luck on your build!
Dan