Stromberg Part Numbers
The carbs in question are the CD150 and CD175 for the 32mm and 40mm Bings.
From Moss Motors, the part numbers are 365-320 and 366-040. Tthey are $20.10 each for the CD150 and $3.95 for the CD175.
(as the owner of a 1976 R75/6 I am most distressed by this)