thanks old's cool - this one falls into category three - one of about 25 ever made to my knowledge. Still checking the authenticity.
I was definitely counting on a professional repair job - wasn't sure how this sort of thing would be approached and/or whether it was a 'beyond repair' situation for this type of frame construction. With lugged frames there are good old school frame makers in these parts who would braze a new tube in without too much problem.