Thanks John,
Compared to the several dozen photos of 1Fs I found, the Craftsman chimney appears to be the correct width. Not sure if any one makes a turned 1F chimney I could replace the warped one with.
I have not seen a photo of 41661 so it is possible it had a slightly slimmer chimney.
I wish more kit manufacturers would include backhead detail. Injectors, water gauges, fireholes, etc, take almost as long to make as the rest of the kit. Luckily I have a good stock of Mainly Trains detailing etches so handwheels and reversing levers are not a problem.
Steve