It has been in doubt what bit of an aeroplane is the aeroplane, certainly in the UK. The CAA from memory did decide that the fuselage should be the aeroplane or someone in the authority did. Common sense says it should be the fuselage but it is easy to take off a registration plate and rivet it to another. Engineers are out here stitching parts together in the hope of making a few bob. The value of old second hand aeroplanes has risen dramatically and I would suspect a rebuild of miscellaneous parts - perhaps following an insurance write off*, may return a profit. The key will be having up to date log books that go back to when new, and without a break, to be married with.
* an insurance write off only reflects that it is cheaper or more practical for the insurer to end the issue with a pay out. Many owners do not register a 'write off' with the authority. Buyer beware!