I do not understand why you cannot adjust the points to give a larger gap unless either the base part of the points is not able to pass through the slot in the carrier body or the spring heal is contacting the condenser terminal and restricting the opening.
However, to confirm the magneto is fitted with the correct cam the slot should be about 2 oclock when the points are fully open. If someone has fitted the wrong cam (from a clockwise magneto) the points will be fully open with the slot about 4 oclock.
I have rebuilt many of these magnetos and never had this issue.
Neil