The 3D print / mock-up clearly indicates a double chimney.
The original 10000 clearly had a single chimney, and for it's first rebuild received a double chimney.
Back to the R3840, R3841 - both grey which keeps the prototypical originality of the beast, are these just going to have the double chimney already shown, or single?
Will the green 'Publicity' locomotive have the double, and the 'greys' the single?
In all initial photos and filming, I only see the double chimney, which suits me, but may not necessarily be correct ...
I think this is one of those 'seen in the flesh' things - when a decision can be made, but for now, a preference would be grey with double chimney.
Al.