The commentary on the six days of creation by Eustathius of Antioch, to which Latino Latini refers in my previous post, is spurious. Indeed only one work by Eustathius (deposed 330 AD by an Arian synod) survives. The text was composed in the late 4th-early 5th century, and makes use of Basil the Great’s work on the same subject, as well as Josephus and even Achilles Tatius. Indeed the work appears to have much more historical interest than the dull title might indicate, since it quotes so many historical sources, at a date well before they appear in manuscript copies.
The work was published in 1629 by Leo Allatius, which is reprinted in the Patrologia Graeca 18, c.708-793. A modern edition by F. Zoepfl exists, with discussion of the codices. Eustathius is found in the Clavis Patrum Graecorum vol. 2, #3350f. The Commentary on the Hexameron is CPG 3393. It appears to be a deeply neglected work.
A search for CPG 3393 in Pinakes, the IRHT database of Greek manuscripts, gives 28 results, including a bunch of mss. in Rome, mostly in the Vatican. Nothing in Naples. But it is unlikely that our ms. is in the well-indexed lists of the IRHT, or it would already be known.
Friedrich Zoepfl, Der Kommentar des Pseudo-Eustathios zum Hexaemeron, in Altestamentliche Abhandlungen X, 5, Munster, 1927.
In Hexameron Commentarius: Ac De Engastrimytho dissertatio adversus Originem… / Ed.: L. Allatius. Lugduni, 1629. PG 18.