Parts M6-44 and M6-45, the two locking cylinders of the 6", 10" and 12" were I think originally parts 9-44 and 9-43 up through the 10E. While designing the 612 & 618 in the mid 30's, they re-did the ram lock. and fitted it to the 10F and all subsequent models.
The coil spring between the two locks might be a good idea but the closed length of the spring would be critical. If the spring goes solid before the lock is fully set, the lock won't set and will slip. One or two shavings or other trash would also prevent it working.
The original parts were probably machined from steel. The new parts were cast from Zamak 5 to save money, not for their non-magnetic properties.