Any of this stuff is going to be inconclusive however supportive it may be.
Any met lab could provide basic chemistry on a piece of metal. You might be able to match it up with the original mill certs, if they still exist somewhere, but it will just identify the alloy and provide the relative fractions of aluminum and whatever alloying elements (copper, manganese, magnesium, etc.) were present in that particular heat. Mill certs will sometimes provide a reading of grain structure and hardness if a material has been heat treated.
Lockheed would have had multiple heats (batches if you prefer) of material available to them, even if they all came from the same supplier. Different heats could end up on the same plane; material from one heat could have ended up on different planes, even one from a builder other than Lockheed. Also, different heats can have identical chemistry, so without an unbroken paper trail to correlate the lab results, no smoking gun.
Further, Alclad was a sheet material and the chemistry would be different from the forging or casting alloys used for heavier structural components.
Since Neutron Activation Analysis is non-destructive, it's a pity that the owner won't allow testing. I know some materials engineers who would love to get a shot at this.
Has NAA been performed on any of the pieces found to date? You could start building a database of known heats based on what you already have. First check for repeatability from area to area on the same artifact, then to similar artifacts, then dissimilar (different gauge but still Alclad) artifacts, then other aircraft (Grace McGuire), etc..