I'm pretty sure its an opened Malcolm hood. If it wasn't, there'd be a large antenna mast top center just behind the canopy; but that's missing. That's a pretty significant clue right there I think.
Here's one of Kid Hofer in almost the same position as Eckfeldt, but on the left side of the A/C:
And one showing the large radio antenna masts on unconverted '51Bs:
Finally, a shot of an opened birdcage canopy - you can imagine seeing this from the front right wingroot, and that's not what the Eckfeldt photo is showing. His photo is missing the top panel and the unopened rightside canopy:
I'm pretty certain we're seeing Eckfeldt in front of his aircraft with a Malcolm canopy installed. I've never found a profile or clear photo (or even a plastic model) of Bald Eagle III with a Malcolm hood though.
The Malcolm was an ETO-only modification, so any of the MTO and CBI '51Bs in game are not historically correct skins.