Thanks for the compliments!
Things you realise only after you post photos: I put the end cap on the barrel on backwards!
I'm trying to decide now how to proceed; aside from some minor stuff there's still the treads and the skirting to apply (for the skirting I'll be using a mashup of the Chieftain and Challenger skirts), and of course painting. I'm wondering if I should paint everything now with the skirts separate, and then attach the treads and the skirting after all the painting is done, or finish the assembly, tracks and skirts and everything, and then paint it, including painting the treads black(ish) again...