I have a pair of matching 276 vertical flange carburettors, that may be suitable for a Douglas Sports machine, they appear not to have been used. Burlen Systems say they are quite rare and could have been made for racing.
One has a brass body the other is made from Masac which was quite common in the day. The brass one did have paint on it before it was cleaned.
You can view these carbs on Ebay, hopefully they will be of some use to somebody.