Honey, I shrunk William!
Sometimes I wish!

Here's a little more progress. I rummaged through my brass stock and soldered up the tubular header tank, which sits just ahead of the observer on top of the engine. This was fed by the gravity tank suspended above and behind the observer's head. If that wasn't enough, the poor fellow sat atop the unprotected main fuel tank. Bloody hell... 🔥
The header tank was a tricky beast to make. The rear portion has a sort of wishbone support that needed to be lap-joined to a short vertical rod, which was threaded through a hole in the main tube and soldered into place. The vertical stack was pinned and soldered too, then the piece was trimmed/repeatedly dropped on the floor until I got a good fit. 👍
The main engine block was painted a mid-grey base colour, then masked and the brass manifold intakes were sprayed with Mr Metal Color 219 (good stuff that). It gives a very welcome steampunk look to the engine. I'll paint the header tank with the same brass colour, then add some brackets and clips from painted decal strip.
Here's a shot of the offending item:

And another shot of it dry-fitted above the engine:
