OK, I've finally got to ask something that I've long wondered about. Why 'Diamond Stacks' on the 470's and 'Straight Stacks' on the 460's, 480's and 490's? I know it's not something that was just done by the D & S because in numerous books I've seen them that way although in Beebe & Clegg's
Narrow Gauge in the Rockies there were some of both. 478 in that book had a diamond stack. In the 60's the 470's were all diamond stack.
If the answer is so obvious please pretend that I am asking a quality question.