The crew of Doc mentioned that magnesium problem as one of the differences between 1945 29’s and today. Pretty scary problem, burning magnesium.
It was a real problem, the top test pilot of the day and a bunch of Boeing engineers were killed on an early flight, engine caught fire and they crashed into a meat packing plant in Seattle. Killed about 20 on the ground, too. There was panic in the government, because they had placed all their eggs in the B-29 basket, it simply had to work.
Were the magnesium engine parts replaced with something safer on “Doc”?