John, a well deserved pat on the back for another excellent tutorial on another fine project!
I have one interjection: Williams also produced the BF-16(15?) in both brass and plastic.
I have a pair of the brass shells in the project queue for detailing and marriage to a pair of Weaver 2 rail decks with dual motors, they are nearly a perfect fit. The caveat is they use a standard wheelbase AAR B truck length, instead of the slightly longer truck.
The Williams brass shells are nearly correct in size & contour, but require quite a bit of detail work.
well done!