Thank you all, again! A mixture of sitting and standing seems to work at the moment.
I did some metal bending. The bunker rear plate was annealed what seems like months ago and conformed nicely. The side etches have to have the front of the tanks formed by bending, and that worked remarkably well. I think I will fit the support cages to the running plate tomorrow, and then sort out the overlays. There’ll be a fair amount of fettling required for the bunker, but I have a nice clear photo of a preserved loco's rump to work with.
I noticed the cab front plate on some locos, originally built with the circular spectacles above the firebox crown, shows where the holes were filled. I need to check whether the chosen loco for this build showed such a feature, or whether it was built with just the side spectacles from new. Photo picking is something I can do in relative comfort!