Neil; Awesome build. Much appreciate the start to finish photos. Are you planning a tandem next?

On the side; Noted that your torching access around the seat lug seems a bit constrainted by the JIG in use. Suggest it might be a good process add to leave the seat tube a few inches longer, moving the JIG bracket further up and out of the way and thus ease the torch. I tend to just leave it full length...others just leave it an inch above the top of the lug. I find the extra bit of seattube as a nice place to slide the brass down into the lug. FWIW!

/K