The last big trip was in 2019 and covered some of the same ground. If you're researching spots for photos, look on Youtube or flickr for photos from that trip. Generally the stops attracted large crowds. It was easier to photograph the train on the move. Also it's more obvious that it's a steam locomotive.
It came by here in November. My plan was to use a bridge over the tracks with a pedestrian walkway. There are electric commuter trains running parallel to the freight line at this bridge, so the pedestrian area is fenced off pretty well to keep people away from the power lines. That limited my position somewhat. Also my background was too cluttered. I didn't have enough time to drive to a better location, but east of the Denver/Aurora area, uncluttered should be easy to find. I did not know they converted the locomotive to run on diesel; I was worried a little about cinders and coal smoke, but that was wrong. I brought two cameras to try out different lens options.