I've updated my own reply here just to bring it up to date.
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For anyone wanting to do a '666/"Lucy" build in 2023 and beyond, this is, until more information comes in, everything we know about the plane.
For those wondering about my sources, I've been researching Jay Zeamer's "Eager Beavers" off and on now for thirty years. The information below comes from personal conversations and interviews with Zeamer, William Vaughan (radio), Ruby Johnston (navigator), Herb Pugh (tailgunner), 16 June 1943 mission copilot J.T. Britton, squadron and group mates, as well as over twenty family members of the regular and 16 June 43 mission crews, who've also gifted me with an extraordinary amount of documentary information. It's complemented by personal archival research, with invaluable assistance from experts on the B-17 and theater including Steve Birdsall and Larry Hickey's publishing crew.
There were sixteen mounted .50s on 41-2666 after it had been field-modified by Zeamer and his crew. (Spares were kept along the catwalks—three for the 16 June 1943 mission to Bougainville—in case of jams; guns were tossed and replaced instead of trying to repair the jam.) Zeamer's personal flight log, the 65th morning report entry for that day, and the gun complement accounting provided in navigator Ruby Johnston's diary confirm this. We know that '666 was outfitted with sixteen .50s as follows:
• 4 - nose: one each in the enlarged side windows (a common field mod in the SWPA); one in the center socket of the Plexi frame; and one mounted either on top of or below the bombardier's deck to the right of the bombardier's chair for Zeamer to fire from his control column. (This was almost certainly modeled after his friend Ken McCullar's arrangement in 41-24521 Black Jack as you can see in the attachment.)
• 2 - top turret
• 2 - radio compartment (field-mod to twins; fairly standard in Pacific B-17Es and Fs by late 1942)
• 2- belly turret
• 4 - waist - field-mod to twins on each side (non-staggered windows)
• 2 - tail
Zeamer's occasional recollection of a .50 through the waist floor aft of the belly turret doesn't comport with his own recorded number and other crew members' recollections. It likely relates to a similar gun installation on the B-26s he flew for fourteen months prior to the B-17. (Note: by mid-1942, all B-17Es and Fs in the Pacific came equipped with .50s, so there was no need for an upgrade from .30s.)
Since photos of Zeamer's modifications have yet to be found, you can get a feel for the paint scheme from volume 1 of IHRA's magnificent history of the 43rd Bomb Group,
Ken's Men Against the Empire. Aviation artist Jack Birdsall's
interpretation of '666 (click on the thumbnail with the aircraft paintings) shows what it would look like with both singles and twins in the waist (they were still uncertain about them at the time of publication). His painting also shows the cursive "Lucy" added to the left cheek days before the 16 June 43 mission. You can see a closer view of that in the other photo attached. For anyone wanting to do a '666 build, until a photo actually surfaces, Fellows' painting remains the safest bet for a guide.
Incidentally, that same page also shows "Reckless Mountain Boys," which was one of the two B-17s Zeamer and the crew flew the most, the other being "The Old Man." They in fact flew only three missions in '666, including the 16 June 1943 mission, which remains the most highly decorated single air combat mission in American history.