John bar Penkaye, as Baumstark summarises him

'Tain't edited, as Yulia Furman has edited books 1 and 9... but there's manuscripts, which I'll get to. But first I'd like some hints as to what's worth translating. As to that heeerrre's Baumstark, again. I've taken the liberty of deleting the folio-references because I'm starting with a different folio. I've lost what little German I ever had, so this is Google Translate - use at own risk.

• Book I begins with the creation of heaven and earth. The first half is devoted to that six-day work; the second recapitulates much more briefly the rest of the biblical prehistory up to the Rapture of Enoch.
• Book II continues the Old Testament story up to the Babylonian exile. It concludes with a chronographic list of the kings of Judah and Israel, and one of the alleged Assyrian-Babylonian rulers, as contrived by the Christian chronograph from Alexandros Polyhistor and the OT, separated by a few sentences about Nabuchodonussor.
• Book III begins with the reign of Cyrus and the return of the Jews from exile. In all essentials, what follows is exactly the content of the second book of the Maccabees. The martyrdom of the seven brothers is told in great detail. On the other hand, for the time being there is no mention of the victorious Jewish struggle for freedom.
• Book IV is not so much a continuation as an addition to the previous one. In the introduction, the author expands upon Old Testament prophecies in general and — without naming it explicitly — on those of the book of Daniel in particular. With the death of Alexander the Great and the division of his kingdom then begins the narrative. A list of the Seleucids up to Antiochus Epiphanes is followed by a retelling of the content of the first and third books of Maccabees, separated by a discussion of the idea that everything God has done to Israel is a prophetic reference to the calling of the Gentiles. After Johannan has explained his intention to break off the detailed account of the events of pre-Christian times, he concludes with a list of the rulers of the Jewish people from Judas the Maccabee to Herod the Great.
• Book V is intended to deal with the influence of demons on mankind as a counterpart to the work of God recognizable in the history of Israel, which demons, with Satan at the head, Johanan divides into three orders. This purely theological explanation concludes with an overview of the worldviews, cults, and vices of various pagan peoples.
• Book VI opens an overview of the Old Testament revelation. At the top is Johannan's list of books recognized by the Nestorian Church of his day as Old Testament scriptures. After stating that these writings have by no means been preserved in their entirety as they were written, and Ezra's editing of the canon provide further material for preliminary remarks of a general nature - Adam, Seth, Noah, Abraham, the Law and the Prophets - he leads to a discussion of the Pentateuch. After the content of the first two books is given in detail and that of the third and fourth is at least briefly indicated, the conclusion is a presentation of the prophetic content, namely Genesis. The promise to Abraham Gen. XII 3, the sacrifice of Ishaq, the sacrifice of Melchizedeq, the story of Joseph, the blessing of Israel and the prophecy of Bi'lam find a particularly detailed treatment in the sense of the typology of Theodore of Mopsuestia and his school.
• Book VII moves on in the path taken by the previous one. The Exodus of Israel from Egypt, the personalities of Moses and Joshua and the Old Testament priesthood are interpreted typologically. The typos is then contrasted with prophecy, the mysterious event with the prophesying word. This is said to have its place chiefly in the Psalter. A detailed explanation of Psalms II, VIII and XLIV is intended to prove this. Finally, the messianic interpretation of the third of these Psalms gives the author the opportunity to present his doctrine of the Trinity and Christology systematically.
• Book VIII first finishes the explanation of Psalm XLIV. The main subject of discussion here, however, is the connection between typos and prophecy, as it appears in the works and writings of the prophets. The explanation of Na'aman's leprosy, Psalm CIV with reference to Melchizedeq, the stories of Elijah and Jonah are treated as prime examples.
• Book IX treats Egyptians, Krionos, Zeus, Demeter, Persephone, Pluton, Dionysus, Aphrodite, Artemis and Apollon, on the other hand Isis, Osiris and Typhon are discussed. Shorter remarks apply to the religions of the "Chaldeans" and the "magicians", the most succinct imaginable to the cults of other peoples, among whom only Edomites and Romans are mentioned by name. Explanations of a purely theologically edifying nature close the most interesting section of the entire work for non-theologians.
• Book X begins the narrative of the life of Christ, which it continues until the beginning of his public teaching. A moving praise of divine mercy and the answering of the dogmatic questions of who Christ is and why he came into the world form the introduction.
• Book XI is dedicated to Christ's public activity, suffering and death, and resurrection. The now fulfilled Old Testament types and prophecies are consistently compiled. It concludes with a discussion of the difficulty arising from Matt. XII 40 compared with the actual dates of death and resurrection.
• Book XII guides the reader from Christ's resurrection until the destruction of Jerusalem by Titus. The apparition of the angels at the Ascension gives the author cause to expand extensively on other New Testament apparitions of angels. After this digression he picks up the thread of profane history where he left it in Book III. From Alexander the Great onward, he reports that the rule of the Hellenistic kings was succeeded by that of the Romans, beginning with C. Julius Caesar, and then gives a chronographic list of the Roman emperors from Augustus to Vespasian, not without repeating the main events, to commemorate New Testament history. The last part of the book is filled with the account of the Jewish war, followed by a review of the prophetic predictions of what has just been told.
• Book XIII deals with the history of the apostles after a broad recapitulation of the previous content of the work. A mention of the magician Simon, which leaves no doubt that the author was familiar with the Roman legend of Peter and Simon, concludes the praxeis of I-X in the first half of these Books. The rest brings legendary information about the origin of the gospels, the missionary activities of the individual apostles and their setting.
• Book XIV outlines the history of Christianity from the death of the apostles to the victory of Islam in Asia. Johannan speaks quite extensively, but in quite general terms, of the Roman persecutions of Christians, briefly of Constantine the Great, in order then to go on to the history of the Church in Persia. The political antagonism between the Roman and Persian empires had long ago led to the bishop of Ctesiphon-Seleukeia being granted an independent position vis-à-vis the Church of the West. The great Persian persecution of Christians then began with Sabur's accession to the throne. After this and the simultaneous Roman-Persian war have been reported, the history of the Arian turmoil and the Council of Nicaea, Julian the Apostata and his successor Jovian follow, introduced by an overview of the heresies from the older Gnostics to Apollinaris and the Macedonians. Below this, after a period of 70 years, the Persian persecution comes to an end after the Romans cede Nisibis to the Persians. Since then the Church in the East has enjoyed peace. In the west, the Arian persecution follows under Valentinian I and Valens, and after a short period of calm under Theodosius and his immediate successors, comes the great christological religious controversy - which is naturally reported with biased one-sidedness. A survey of the dogmas of the three denominations which emerged from the struggle — Nestorians, Chalcedonians, Monophysites — closes the history of these turmoils, and the Councils of Ephesus and Chalcedon. A few words follow about the origin of monasticism in Egypt and an equally vague account of the fall of the Persian Empire and the victorious course of the Arabs, which ends in a description of the extent of the new Mohammedan world-empire.

... I'm skipping Baumstark's loooong summary on Book XV since we know that already; in my opinion he were better to have translated it himself instead.

Baumstark lists some parallels, which Bar Penkaye may have used. Baumstark doesn't come up with much. Book XII used Josephus' Jewish War. We own Josephus' Book VI in Syriac as "5 Maccabees", at the Biblioteca Ambrosiana in Milan: Bedjan (1905), 770-837; also cf. footnotes 32-4. Bedjan thought that the Milan translation was poor. Maybe Bar Penkaye, who knew Josephus for Josephus, owned a better translation. One does wonder about which Josephus.

Baumstark noted also a pile of Christian apologetic: Aristeides c. 9-12; Justin Apol. I c. 54; Tatian c. 8-10, 21, 32; Athenagoras c. 17-22, 28-30; Ambrosius (?) Logos pros Hellenas c. 1-3 (Spic. Syr. 38-41), Ps.-Meliton Spic. Syr. 24 f.; Quadratus may be here as well, and of course Theodore of Mopsuestia. We may assume Bar Penkaye had all of it via Syriac or through a Syriac intermediary.