Given the restrictions, I guess what I would do would be to go through all of the great libraries of the ancient world.
Alexandria, Egypt and Constantinople are the two big ones I have in mind.
Most people probably don't know about how few manuscripts we have of many, many ancient texts. I would look specifically for Biblical manuscripts, books by Democritus (an early atomist who was well regarded, but we don't have any of his works), the dialogues of Aristotle (believe it or not, most of Aristotle's philosophy was written in dialogue form like Plato, in fact, some say he wrote better dialogues than Plato. The works we have now are something like lecture notes), and anything from the presocratic philosophiers (we only have quotes of their works, not any manuscripts).
If I could change history, I would start the industrial revolution in ancient Athens.
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Iamscientist
Truth is, I'm not a scientist. I'm an analytic philosopher, but we like to think we're scientists.