Pictures for thought. All SA's and Classics are constructed the same. In 73-74 Lincoln used inner aluminum windings on the shunt field coils. But like I have said before, and Tom Fowler can agree,thousands of shunt field coil sets have been replaced in these machines over the years. So it is hard to determine by age what 73-74 machines still have aluminum shunt field coils.
Since I have worked in this field, 19 years, the code numbers we have seen with faulty field coils is 7307 and 7789. And our shop has replaced shunt field coils in approx 113 of these machines.