"If" there was an engine fire?
Shouldn't that be "whenever"?
I was once privileged to be on board the CAF's FiFi. First a good look round, then the engine start sequence. But we had to disembark before flight, due to the FAA's observations after the Marauder accident.
But what I clearly remember was the 'diagnosis of engine failure by smoke' chart in the back. Various diagrams of smoke belching from poorly motors allowed diagnosis of engine failure, supercharger failure or whatever.....
Presumably the DC-6B's passengers could make similar observations?