Hi--this is a lovely bike!
I am in the process of building up a casseroll myself and have run into a hitch. I am installing brifters, but just realized that there aren't any derailluer bosses on the downtube--there are just the bosses for downtube shifters. I notice on your build that you seem to have an attachment that slips over the downtube shifter bosses, however. Where can I get these, and what are they called?
Thanks so much for your help.