You are a little late as the claim that the 1st. c. LXX contained the Deuteros has been shown to be presumptuous, as well as problematic.
The only manuscripts of the Septuagint we have that contain books of the Deuteros were made after the the Hexaplar recension (one of many revisonary works, and in which some meaningful changes were made in the texts themselves) and include the Codex Vaticanus from the 4th century CE and the Codex Alexandrinus of the 5th century. "These are indeed the oldest surviving nearly complete manuscripts of the Old Testament in any language; the oldest extant complete Hebrew texts date some 600 years later, from the first half of the 10th century. (Ernst Würthwein, The Text of the Old Testament, trans. Errol F. Rhodes, Grand Rapids, Mich.: Wm. Eerdmans, 1995) The various Jewish and later Christian revisions and recensions are largely responsible for the divergence of the codices." (Jennifer M. Dines, The Septuagint, Michael A. Knibb, Ed., London: T&T Clark, 2004) - https://en.wikipedia.org/wiki/Septuagint#Manuscripts
Also,
Manuscripts of anything like the capacity of Codex Alexandrinus were not used in the first centuries of the Christian era, and since in the second century AD the Jews seem largely to have discarded the Septuagint…there can be no real doubt that the comprehensive codices of the Septuagint, which start appearing in the fourth century AD, are all of Christian origin.,,
There is no evidence that elements of Diaspora or Palestinian Judaism had an expanded Septuagint canon distinct from the twenty-two book Hebrew canon, and the historical probabilities weigh heavily against such a supposition. There is also no evidence that the ante-Nicene church received or adopted a Septuagint canon although it did apparently consider the Septuagint to be inspired and its text-forms to be superior to those of the masoretic Bible.'" (Roger Beckwith, [Anglican priest, Oxford BD and Lambeth DD], The Old Testament Canon of the New Testament Church [Eerdmans 1986], p. 382, 383)
And if you are going to use these copies of the LXX for a canon then you have a real problem, for it means you must exclude some that Rome holds as canonical and include some that it does not. For the Psalms of Solomon, which is not part of any scriptural canon, is found in copies of the Septuagint as is Psalm 151, and 3 and 4 Maccabees (Vaticanus [early 4th century] does not include any of the Maccabean books, while Sinaiticus [early 4th century] includes 1 and 4 Maccabees and Alexandrinus [early 5th century] includes 1, 2, 3, and 4 Maccabees and the Psalms of Solomon).
Nor is there agreement between the codices which the Apocrypha include...Moreover, all three codices [Vaticanus, Sinaiticus and Alexandrinus], according to Kenyon, were produced in Egypt, yet the contemporary Christian lists of the biblical books drawn up in Egypt by Athanasius and (very likely) pseudo-Athanasius are much more critical, excluding all apocryphal books from the canon, and putting them in a separate appendix. (ibid, Beckwith)
Likewise Gleason Archer affirms,
Even in the case of the Septuagint, the apocryphal books maintain a rather uncertain existence. The Codex Vaticanus (B) lacks [besides 3 and 4] 1 and 2 Maccabees (canonical, according to Rome), but includes 1 Esdras (non-canonical, according to Rome). The Sinaiticus (Aleph) omits Baruch (canonical, according to Rome), but includes 4 Maccabees (non-canonical, according to Rome)... Thus it turns out that even the three earliest MSS or the LXX show considerable uncertainty as to which books constitute the list of the Apocrypha.. (Archer, Gleason L., Jr., "A Survey of Old Testament Introduction", Moody Press, Chicago, IL, Rev. 1974, p. 75; http://www.provethebible.net/T2-Integ/B-1101.htm)
The German historian Martin Hengel writes, “Sinaiticus contains Barnabas and Hermas, Alexandrinus 1 and 2 Clement.” “Codex Alexandrinus...includes the LXX as we know it in Rahlfs’ edition, with all four books of Maccabees and the fourteen Odes appended to Psalms.” “...the Odes (sometimes varied in number), attested from the fifth century in all Greek Psalm manuscripts, contain three New Testament ‘psalms’: the Magnificat, the Benedictus, the Nunc Dimittis from Luke’s birth narrative, and the conclusion of the hymn that begins with the ‘Gloria in Excelsis.’ This underlines the fact that the LXX, although, itself consisting of a collection of Jewish documents, wishes to be a Christian book.” (Martin Hengel, The Septuagint as Christian Scripture [Baker 2004], pp. 57-59)
Also,
The Targums did not include these books, nor the earliest versions of the Peshitta, and the apocryphal books are seen to have been later additions, and later versions of the LXX varied in regard to which books of the apocrypha they contained. “Nor is there agreement between the codices which of the Apocrypha include. (Eerdmans 1986), 382. The two most complete targums (translations of the Hebrew Bible into Aramaic which date from the first century to the Middel Ages) contain all the books of the Hebrew Bible except Ezra, Nehemiah and Daniel.
And Cyril of Jerusalem, whose list rejected the apocrypha (except for Baruch) exhorts his readers to “read the Divine Scriptures, the twenty-two books of the Old Testament, these that have been translated by the Seventy-two Interpreters,” the latter referring to the Septuagint but not as including the apocrypha. (http://www.bible-researcher.com/cyril.html)
And that the smaller canon was that which was held by those who sat in the seat of Moses, and which is the only one quoted from by Christ, and referred to as "Scripture, "it is written, etc,." in the NT, is what the weight of testimony shows,
"In all likelihood Josephus' twenty-two-book canon was the Pharisaic canon, but it is to be doubted that it was also the canon of all Jews in the way that he has intended." (Timothy H. Lim: The Formation of the Jewish Canon; Yale University Press, Oct 22, 2013. P. 49) By the first century, it is clear that the Pharisees held to the twenty-two or twenty-four book canon, and it was this canon that eventually became the canon of Rabbinic Judaism because the majority of those who founded the Jewish faith after the destruction of Jerusalem were Pharisees. The Jewish canon was not directed from above but developed from the "bottom-up." (Timothy H. Lim, University of Edinburgh: Understanding the Emergence of the Jewish Canon, ANCIENT JEW REVIEW, December 2, 2015)
which is affirmed in Catholicism: “the protocanonical books of the Old Testament correspond with those of the Bible of the Hebrews, and the Old Testament as received by Protestants.” “...the Hebrew Bible, which became the Old Testament of Protestantism.” (The Catholic Encyclopedia>Canon of the Old Testament; htttp://www.newadvent.org/cathen/03267a.htm) The Protestant canon of the Old Testament is the same as the Palestinian canon. (The Catholic Almanac, 1960, p. 217)
Yet teachings and or history found in the Deuteros 9among other sources) can be alluded to and some of its teachings and history validated (and we can both reference sources for some of what they say even if we do not fully concur with all they say).