As a physicalist I don't think this mind/body dualism is accurate.
You're correct to identify a dualism here but you're misunderstanding what it is. The "body of the Tathagata" is not the mind and it certainly isn't an individual soul/atman; instead, it's the cosmic "dharma body" of a transcendent buddha, which in Theravada is identified with the dharma in the sense of the body of Buddhist teachings, and in Mahayana is a polysemous term referring to the Buddhist teachings, the collected body of experiences (also called dharma) of a buddha, and the "body" of reality itself (sunyata).
So would it be accurate to call this body/Body dualism? With the first term being the egoistic body which leads to smallness and death, and the second term being the enlightened Body which is the source of wisdom and life?