"How/when did 498 get to Sargent to join up with 495 and 499?"
This appears to be one of the busy times when helper engines and crews were stationed at Sargent. On Februry 23, engine 490 was in that category. It helped a Sargent turn make two trips to Marshall Pass.
On February 22 59 loads moved east out of Gunnison, February 23 72 loads moved east out Gunnison, and again on February 25 another 59 loads moved east out of Gunnison.
On February 23 engine 498 was one of three engines taking the 72 loads east out of Gunnison. It was used as one of the helpers making 2 turns to Marshall Pass. Each turn had 18 loads. After the last turn 498 returned light to Sargent and stayed as "assigned helper" On Febuary 24 it was again used on 2 turns, again each had 18 loads.
It shows up as staying at Sargent for the next few days.
Jimmy