A Mitsubishi A6M3 has returned to airworthy status, albeit with a P&W R-1830 engine, a DC-3 prop, the prop spinner is from a Lockheed Super Constellation, and there are only 200 original parts in this "restoration".  Still, it is now flying!

https://www.militaryaviationmuseum.org/the-zero-flies/

Edited May 9, 20251 yr by stans

Most of the restorations these comming out these days are whats called data plate restoration ie the only thing original is the data plate and maybe some small parts. 80 years of exposure to the elements has made most original parts unusable if a wreck was recently recovered. This is especially the case for Japanese aircraft whos aluminum was extremely thing to save on weight. Even back during the war it wasn't uncommon for a pilots foot to go through the wing due to the skin being so thin.

Edited May 9, 20251 yr by z06z33

Only 200 parts is pretty good going. 

It's a interesting question though. This thing;

...spent 46 years buried under a beach at Dunkirk. The only original part on it now is indeed the data plate. Everything else are modern parts. It's possible to build a 'new' Spitfire if you have five or six million lying around.

Also, old aircraft end up having major parts of the airframe replaced over time anyway. The oldest flying Tiger Moth G-ACDC has never been 'restored' as such but it's thought the only original part of this 92 year old aircraft is the rudder post.