Is 585 hallmarked enough or does it need 14ct hallmarked
Interesting question. This is an Italian made item of jewellery so wouldn't be expected to carry UK hallmarks. 585 is a recognised stamp for 14ct gold so I imagine the authenticators will probably accept it. That said, for an item of this value perhaps they may want to be ultra careful.
As a last resort you could always submit it for hallmarking in the UK. I once took a supposedly 14ct Egyptian made necklace to the Birmingham assay office. Unfortunately it turned out to be 9ct!