The Last Supper was the institution of the Eucharist, essentially the first act of transubstantiation. In breaking bread and sharing the cup, the Twelve Apostles received the real body and blood of Christ.
The Lord Jesus Christ, Himself the guest and banquet, is both the partaker and what is eaten.
Christ first fulfilled what He required others to observe. For example, Christ instituted baptism by being baptized Himself, in the same way He would have instituted the Eucharist by partaking in the Eucharist Himself.
If you look at transubstantiation, however, I do not believe the term “literal” is going to be helpful for understanding. Transubstantiation is not something that occurs in nature — it is a way of describing how Christ is uniquely present in the Eucharist — the observable characteristics of the bread and wine remain (the “accidents”) but the inner reality of the bread and wine (their “substance”) changes into Christ’s body, blood, soul and divinity. Nowhere else in nature or theology does such a change occur— it is unique to the Eucharist.
Note that eating the body and blood during the Eucharist is not the same as if someone hacked off a piece of meat off of Jesus’s earthly body and cannibalized his flesh.
But that's exactly the argument you make from John 6. You've used the words chew and nash IIRC. You've said the Jews and His disciples understood it that way.
You've just contradicted your own position on this issue.