Your arguments about Melchizedek who is said to be the King of a Canaanite city called Salem are nothing more than a series of improbable conclusions based on wishful thinking and why you would think I would have given it the slightest consideration is beyond me.
As you consider yourself a student of Hebrew tradition, I thought that you would be at least interested in the Hebrew tradition of Melchizedek being the title given to Shem. Perhaps more research on this probability from yourself is required.
Nevertheless, Abraham is a direct descendant of Shem who were both alive at the same time. Shem being the patriarch of the future Israelites would have been the original source for the flood story and I see no reason why Shem would not have related it to Abraham, the father of nations, first hand.
To use your turn of phrase, the proposition that Moses received this story from GOB is unsubstantiated and is nothing more than a series of improbable conclusions based on wishful thinking.
Therefore, Shem tells Abraham (logical), or GOB tells Moses (fanciful).
I find your comment, "Why you would think I would have given it the slightest consideration is beyond me," to be condescending. But, it's impossible for a literal bible believer to have an open mind or think logically on these matters, isn't it?