old iron wrote:
The next question is whether these judgments applied to wood also apply to metal. Does a P-51 with an original engine, some instruments and a data plate count as a "restoration?" I would say categorically no, especially where the engine and data plate are not physically related to the same aircraft. The only thing that is in the original context is the data plate by itself. It would be to my mind a full-sized and wonderfully detailed model of the original = a reproduction. It presents but does not preserve the original aircraft.
In the US it comes down to some form of ownership. That can come from recovering a WWII crash site where you can document what it was and prove/get ownership. No one else can have a claim to it. Or it can come from buying paperwork.
So basically there isn't an amount of original metal that is even required in some respects.
Anyone could build a homebuilt of any WWII fighter and register it as an Amateur Built Homebuilt and get it registered in the Experimental Category. Gerry Beck did this with his P-51A.
Again as far as FAA Airworthiness goes Restoration isn't really a legal term.
Restoration and the viewpoint your coming from is more a Museum/Collector/Purist thing. Not really a Fly an Airplane/Legality/FAA thing.
If you can get the FAA to register a P-51 by some form of proving ownership, then any collection of parts you put together have to follow workmanship and standard practices as approved by the FAA and signed off by a FAA designated Mechanic and IA along with conforming to the TCDS and following P-51 manuals. Then you have an AIRWORTHY P-51. The FAA is concerned with AIRWORTHINESS after the ownership of some form have been proven. A questionable Dataplate won't cause an A/C to crash but the sky is the limit for how things are done, improper materials, bad workmanship, poor piloting, lack of experience, ect. That is where the FAA Rules and Regulations along with quality workmanship and good training along with keeping current in your flying become the focus of most of us involved in these Warbirds.
Most owners and pilots don't have a big concern with linage as much as they want to fly a really cool/exciting/high performance A/C.