I would be more concerned that the new brake cams don't fit either the original backplates or the levers. Either the Barleycorn bits are wrong by incorrect manufacture/ incorrect order/supply or there is something wrong with the existing brake set up. Better to modify pattern parts than chop pieces from an original factory part, but some dialogue with Barleycorn to get to the bottom of this conundrum would be my first thought. Previous posts would indicate they are very interested in supplying parts that fit.
The absence of a nipple is of no real consequence, and would add another machining operation and unnecessary additional cost.
Swarfy.