You pretty well got the list, John! My experience in the few places I worked..Durango..Ogden, Provo..and Salt Lake was that most of the time in these locations, we pretty much all helped each other out....at least until some craft got the notion that the rr was trying to eliminate their craft. And that idea was usually put to rest fairly soon. Helper was pretty much the same. That said..I always heard that Denver was more adamant about not crossing craft lines. Never worked there..so don't know.
Not sure when the boilermakers and pipefitters made their exit, but they were pretty much the first to go...cab carpenter work was turned over to the carmen, at least on the utah side pretty early, as well.
Doug