I've also had some information from Marcus in response to queries as to whether or not the Foundry castings would be smaller than the original Citadel, and if Foundry are using production castings as masters. Marcus writes:
As far as I'm aware the moulds we would cast masters from are the very same moulds that the original greens were pressed in, so we should be able to make models at least as chunky. However, we should still have the original set of master castings and I would hope that nothing has happened to any of these over the years that would make us need to cast more. Theoretically, since production moulding and casting techniques should have advanced in the decades since the models were originally released, we should be making them both chunkier and crisper!