URR #30 question among others

Roger:
Was URR #30 the locomotive that had to be shipped over Baxter Pass in pieces due to its size and the tight curves? As I recall, if this was the locomotive, it was also cut up at Rainbow or Dragon for the same reason. All a shame, as it had very nice lines.
Earl (and others), what was the technical breakthrough that made the K-36's possible? Why didn't locomotives of this size get made in the early 20's?
This string and the one on K-28's caused me to realize that the 470's were not that much bigger than K-27's--at least in terms of tractive effort. Givent their modernity, I had always thought K-28's could pull lots more, but I guess the Grande had to wait for the K-36's.
It seems that when new power arrived on the narrow gauge, it went to Marshall Pass to cover the coal and limestone traffic going into Salida. When the 470's arrived, how were they assigned over the system? 474 obviously was the Crested Butte engine, and it seems like 2 locos were assigned to the Gunnison passenger (479 being one), and two to the Durango passenger and Chile Line each. That leaves three engines to roam the system. Did they cover through freights? Were they assigned to Sargents? Just wondering.
Keith