"And Melchizedek king of Salem brought forth bread and wine: and he was the priest of the most high God.
And he blessed him, and said, Blessed be Abram of the most high God, possessor of heaven and earth:
And blessed be the most high God, which hath delivered thine enemies into thy hand. And he gave him tithes of all."
The footnote says Melchizedek in Hebrew means "king of righteousness". When I read that he "brought forth bread and wine" I could not help but think of the sacrament. In the Joseph Smith translation it says "and he brake bread and blest it; and he blest the wine, he being the priest of the most high God."
I had heard that Shem, son of Noah was identified as Melchizedek. I went on a scripture chase and other outside sources to find that reference. It was even in the Ancient History of the Jews. So, it wasn't just Joseph Smith that identified Shem as being Melchizedek that Abram paid his tithes too.
Shem lived to the age of 600. He was 390 years old when Abram was born. Abram would have been around 54 years of age when this battle happened and he met Melchizedek. I read in Doctrine & Covenants 138:41 "Noah, who gave warning of the flood; Shem, the great high priest; Abraham, the father of the faithful; Isaac, Jacob, and Moses, the great law-giver of Israel;"
As I sat and pondered on this, the fact that Abram name was changed to Abraham and Sarai to Sarah by God, I could find no reason inside myself to not think God capable of changing Shem's name to Melchizedek if he saw fit. For new names are part of God's covenants with his people.