Possible sources of fire?
Depending on how modified this aircraft was from original, just inside that open crew door on the left behind the pilot's seat were the two carbon-pile generator regulators which were almost impossible to balance. All of the load would sometimes go on the one, and the only way to get the other one woken up was to switch off the one taking all the load. They could get quite hot, and must be considered a source of fire in this case, I would have thought.
Also the two aircraft batteries, conventional wet-cell, are mounted below the cockpit floor, so plenty of possibilities, IMHO.