Would like to offer a couple of comments.
FYI Great Britain is about to ban the use of coal in steam locomotives, and similar machinery.
The US and Canada is well on the way to that.
So it's oil, or your engine can no longer run.

I'm told the UP shop crew had access to the original UP oil conversion drawings for that class of engine. Apparently only one was modified, and it was later converted back to coal.
They used those drawings for the conversion, which includes the use of a adjustable front burner, and lining the firebox with firebrick.

The firebrick evenly distributes the heat over the entire firebox.

As to a few people demanding the engine 'prove' itself, by hauling a max load up a steep hill, give your head a shake.

Just my opinion, of course.