Dom, my friend and brother, your goal is noble. You want your friend to see the light of Jesus and believe and live for Him.
Jesus, who credited the work to Moses, said, "If they do not hear Moses and the Prophets, neither will they be convinced if someone should rise from the dead.” Luke 16:31.
In other words, your friend has marshaled his arguments against the truthfulness and validity of Scripture. He won't hear the Law and the Prophets. Jesus arose from the dead; he won't be convinced about Jesus, either -- at least not from argument about the authenticity of manuscripts, etc.
It may be that --- even unwittingly --- he wants to spoil you more than he is interested in hearing truth. Julius is spot on. The issue is not "who wrote the Torah?" The issue is "Who is Jesus and what will you do about Him?"
The simple, straightforward truth is that he has gone to great effort to discredit a faith that he already rejects! What for? Is he soothing his conscience, perhaps? Hasn't Paul written:
18For the wrath of God is revealed from heaven against all ungodliness and unrighteousness of men, who by their unrighteousness suppress the truth. 19For what can be known about God is plain to them, because God has shown it to them. 20For his invisible attributes, namely, his eternal power and divine nature, have been clearly perceived, ever since the creation of the world, in the things that have been made. So they are without excuse. 21For although they knew God, they did not honor him as God or give thanks to him, but they became futile in their thinking, and their foolish hearts were darkened. 22Claiming to be wise, they became fools, 23and exchanged the glory of the immortal God for images resembling mortal man and birds and animals and creeping things.
He is suppressing the truth, not denying it. He is patching over the work of the Law in his heart with "wisdom" and a "glory" of "mortal man". Why? Because God has made Himself plain already. What power is there against such a man? Paul said it in verse 16:
I am not ashamed of the gospel, for it is the power of God for salvation to everyone who believes, to the Jew first and also to the Greek. 17For in it the righteousness of God is revealed from faith for faith, as it is written, "The righteous shall live by faith.”
Brother, my prayer is that you will shift gears on him. Honest intellectual inquiry and debate about the sources of our scriptures is fine. But, it doesn't convert dead men into live ones. The only power for your friend is the power of the gospel. Only through believing Jesus does "He [give] power to become the sons of God"
Long ago, while not dismissing my curiosity about the history of the Bible and while actually feeding into it, I came to the conclusion that I believe the Bible because what it says about ME is correct: All have sinned; the heart is deceitful and desperately wicked; I lived in the passions of my flesh, carrying out the desires of my body and mind. This book that never met me pegged me. This book that never read my mind and heart nonetheless described me perfectly. Only God can do that. No man has ever passed from death to life by believing and following anyone other than Jesus Christ. There is no other name given under heaven among men by which we must be saved.
Stick to his issues with Jesus and let the Holy Spirit do the convincing within him. Pray, fast, call out his name to God for a heart of faith.