Fine work! It is very heartening to see a rescuee returned from a sorry state to proper and indeed truer condition.
An impressive run, too – no shortage of steam, and she certainly makes light of what seems a suitably stiff bank for the Pennine foothills (or Oregon forests!). I noticed you'd notched down for it.
The big ones were probably slow because they had to be driven slowly, expected to drag heavy trains along often very indifferent, sometimes temporary, track where galloping along could have proved Very Unwise.
I studied the spark-arrestor drawings and its parts quite carefully. I'd often wondered those characteristic American wood-burner precautions – vital in forests of course – worked: essentially a very simple cyclone, slowing the embers and throwing them sideways out of the exhaust stream. What do the four holes in the bottom of the central tube do, though? On full-size, burning wood, I'd have thought they would soon become buried in ash.