The Ascension

"No, they are not the same thing. Please show me any traditional Catholic source such as the Catechism or maybe the Summa Theologica that expresses this idea."

First, I didn't say they were the same thing. I said that they are two ways of talking about the one thing. I also wouldn't say that the heads and tails sides of a coin are the same thing, but they're not completely separate things either.

Look at all the heresies the Church has fought against. Early on, in antiquity, the fight was agaisnt any sort of gnosticism, which argued that salvation was the soul's freedom from the body (see, for instance, the much publicized "Gospel of Judas"). We fought against Christological heresies that sought to make Jesus a strictly spiritual God. We fought against later sorts of gnosticism, like Manicheism, which saw spiritual and bodily as radically opposed. Around the turn of the millenium, what were the two big heresies? One claimed that the Eucharist was a symbol, that it only operated on faculties of the soul, such as on reason, that it was just a spiritual thing. (I'm sure you're familiar with this heresy's re-emergence). The other heresy argued for a physical transformation, that the change in the Eucharist was specifically into the literal, physical flesh of Jesus. Both of these dualistic heresies are condemned by the Church. (Transubstantiation relies on Aristotelian metaphysics, which I'll get to in a second). And let's not forget the last great heresies, those of Luther et al. Every page of everythign Luther wrote is dripping with body-soul dualism. The body is just this thing the soul has. Why fast? Why go on pilgrimage? Why do any works at all? Works are done by the body, and therefore don't matter. Faith alone is done by the soul alone.

Why do you think we used to specifically burn heretics at the stake? We didn't draw and quarter them or hang or shoot, etc. Not that killing is ever right, but why would the Church chose a means of execution which destroys the body? Do you think it's a coincidence that most heresies were dualistic and that most heretics were punished with the destruction of their bodies? And regardless of what the CCC says now, burial in consecrated earth was a big deal. For instance, during the Elizabethen reforms, it was illegal to be buried in consecrated earth, so when a recusant died, their family wrapped them in a shroud with a handul of dirt blessed by one of the preists-in-hiding.

A couple instances of anti-dualism in the Church.
First, why do you think we venerate Mary? When did Marian theology start emphasizing her importance? In the fight against dualism. Mary carried the body of Jesus around in her womb, which is part of her body. For this, we call her the Mother of God. We don't call her, as some Protestants do, someone who just happened to physically carry around Jesus, or "Yeah, but not really the mother of God, she's just the mother of Jesus' human body."

Second, look at what Augustine said in the Enchiridion, 91, "This is why their bodies are called "spiritual," though undoubtedly they will be bodies and not spirits. For just as now the body is called "animate" [animale], though it is a body and not a "spirit" [anima], so then it will be a "spiritual body," but still a body and not a spirit...For there will then be such a concord between flesh and spirit—the spirit quickening the servant flesh without any need of sustenance therefrom—that there will be no further conflict within ourselves." Then take into consideration his philosophical underpinnings. He's a neo-Platonist, saying clearly that we will still very much be with our bodies. Think about how bizarre it is for a Platonist to grant even that much. Even a Platonist can't imagine a resurrection that isn't in the same body as in this life (as he clarifies at the start of 91).

I don't know if it's ever very clearly stated in the Summa, but I think that it's safe to say that that's Thomas' position. Thomas is Aristotelian; so we ought first understand what it would be to think about the issue as an Aristotelian and not as a Platonist. For Aristotle, any specific thing is an embodied form (with a little 'f,' as opposed to the Form, with a big 'F'). You can talk about the form as distinct from the embodiment thereof, but you can't talk about thing without it's embodiment. Anything is an embodied form, including a human being. The form, the final end, etc. of a person happen in a body.

As for what St. Thomas says (Prima Pars, 76.5) :
"On the contrary, The Philosopher says (De Anima ii, 1), that "the soul is the act of a physical organic body having life potentially."
I answer that, Since the form is not for the matter, but rather the matter for the form, we must gather from the form the reason why the matter is such as it is; and not conversely. Now the intellectual soul, as we have seen above (Q[55], A[2]) in the order of nature, holds the lowest place among intellectual substances; inasmuch as it is not naturally gifted with the knowledge of truth, as the angels are; but has to gather knowledge from individual things by way of the senses, as Dionysius says (Div. Nom. vii). But nature never fails in necessary things: therefore the intellectual soul had to be endowed not only with the power of understanding, but also with the power of feeling. Now the action of the senses is not performed without a corporeal instrument. Therefore it behooved the intellectual soul to be united to a body fitted to be a convenient organ of sense..."

That is, the soul and the body are united. This is not to say that they're the same thing (i.e., monism), but only that they are united. The soul, without the body, simply can't do all of the things that souls do. You seem to be rasing, roughly, the following objection, form the same article:
"Objection 1: It would seem that the intellectual soul is improperly united to such a body. For matter must be proportionate to the form. But the intellectual soul is incorruptible. Therefore it is not properly united to a corruptible body."
To which the angelic Doctor replies:
"Therefore we answer otherwise by observing that in matter two conditions are to be found; one which is chosen in order that the matter be suitable to the form; the other which follows by force of the first disposition. The artisan, for instance, for the form of the saw chooses iron adapted for cutting through hard material; but that the teeth of the saw may become blunt and rusted, follows by force of the matter itself. So the intellectual soul requires a body of equable complexion, which, however, is corruptible by force of its matter. If, however, it be said that God could avoid this, we answer that in the formation of natural things we do not consider what God might do; but what is suitable to the nature of things, as Augustine says (Gen. ad lit. ii, 1). God, however, provided in this case by applying a remedy against death in the gift of grace."

Dualism, the separation of body and soul, is remedied for by grace. Perhaps in our fallen states dualism makes sense and is phenomenologically valid, but as God created us, dualism is pure nonsense. The two things are united things, not separate things.

Lastly, CCC 365: "Spirit and matter, in man, are not two natures united, but rather their union forms a single nature." Human nature consists precisely in the embodiment of the form of being human.