Bish: here are the sprues from the Airfix B-17G with unused parts.
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Upper left are cowls for the early Forts--B through D models. I think they are very accurate for those versions. Just don't need them in the kit for an F or a G. The later cowls, for the E through G models are not so accurate.
Next to them are the horizontal stabilizers for the early models, and below them in the center are the props for the early forts. Over to the right are various parts also for the early Forts, including floors, seats, bulk heads and even the lower gun tub/turrent that wasn't used after the D model.
I will post pcs of a B-17B I finished a few years ago, along with a G model, both from Academy.