Here are a few shots of the sequence I mentionned.
1. TT-HT is brazed and ST mitre is checked
2. ST is tacked and checked for twist
3. check for DT fit (with dummy BB on the other end), then tack DT
4. braze ST then DT (it's a mixte)
5. nice stress-free fit (stuff did move when brazing so I had to coldset the ST a bit)