use any parts you can find, that's the beauty of interchangeable parts and the machine age... and that is the only way this B 17 could be built, from the major assemblies of at least 4 planes

The fuselage was rebuilt from parts of B-17Gs 44-83722 and 44-83316. The inner wing panels came from 44-85813, and the outer wing panels from 44-83722. The vertical stabilizer came from 44-83525. The nose compartment and the radio room compartment had to be built as a new structure.

 The forward fuselage is externally complete. Most aircraft systems such as electrical, hydraulic, and control cables have yet to be installed and most will wait until the fuselage is joined at Station 6 and/or the inner wing panels are attached and the airplane is up on its landing gear.

44-85813 was severely damaged in an April 1980 accident at Bear Pen, South Carolina, while operating as an air tanker. The fuselage was largely burnt out. The wings, though damaged, were relatively intact.

Both outer wing panels, as noted earlier, have come from atomic test target aircraft 44-83722. This airplane was dragged off the Nevada Test Site in 1965 and subsequently used for parts to support air tankers

The restoration project began in 2005 by Jerry Schiffer, who shortly afterward was killed in an airplane accident. However, his three adult children (Dave, Eric, and Andrea) took up the project and have driven it forward over the past eighteen years.

https://warbirdsnews.com/warbird-restorations/b-17g-champaign-lady-restoration-update-summer-2023.html#google_vignette

It's not likely to get in the air for another decade, if everything goes well, but it's interesting to learn that this B 17 is in progress, as I hadn't heard of it before.