You think the Septuagint is a "significantly different version of the Bible"? I thought it is simply a Greek translation of the Hebrew OT with some literary adjustments made for Greek idioms etc.
It’s a translation of *a* Hebrew OT. Let’s say certain key phrases and passages are different. For instance, where the Hebrew says, “a young maiden will give birth,” the Greek specifies that a virgin will give birth. Now, “young maiden” presumes “virginity,” if not, then the young maiden is a fornicator.; how would that be a miraculous wonder from God?
But for just how different they are in places, consider this passage from Luke, which is much closer to the Septuagint version:
He has sent me to proclaim freedom for the prisoners
and recovery of sight for the blind,
to set the oppressed free
Compare this to a translation of Isaiah 61 made by the same translators of the same bible, taken directly from the version of the Old Testament used by Jews, today (the Masoretic Text):
He has sent me to bind up the brokenhearted,
to proclaim freedom for the captives
and release from darkness for the prisoners