This comment remains extremely relevant. If No. 4 was feathered and No. 3 had some other issue taking it to a bad prop position...
Valid point on the engine if it couldn't be feathered - it's hard to speculate what caused the issue - engine 4 with 800+ hours or engine with 0 hours before overhaul. And if indeed the 4 or 3 couldn't be feathered (or both) then it was just a math game then.
I suspect the throttle quad was burnt/melted beyond any post-crash inspection possibilities. But I could be wrong and they just have a charred/burnt cockpit.
I'm with Vraciu - the FE will definitely tell the story on this for us as long as he can remember what happened.
Another point, even with 36'000 hours of flying, there isn't much info on how many hours in the B-17 both had. If we're talking just a couple hundred, then we're dealing with an inexperienced in-type crew are we not?