Assuming the have a scale of such capacity, they can do an initial weigh-in by the pallet, because it’s just math. If there are no significant problems, they can compare what a pallet of gold should weigh with what it does way. Then, within a margin of error, they should be able to determine if there is a problem.
From there, they can start to go through the process of checking every gold bar using more accurate techniques to determine if there is a problem.
It might take four years to analyze every bar, but I think it’s necessary after 50 years.
Gold doesn’t come on pallets. And moving it is quite difficult / time consuming / labor intensive. That initial weigh-in would be by the melt, which is how the bars are serialized.
But the whole thing is still do-able inside of a couple of years at most.