Does he say that Vishnu & him are the same? Interestingly, the word "narayana" never occurs in the Gita. Does he say that the other Gods are all parts of him?
Yes, Krishna did say in the Bhagavad Gita that He is Vishnu. The Bhagavad Gita 10.21 states:
Of the Adityas I am Vishnu, of lights I am the radiant sun, of the Maruts I am Marici, and among the stars I am the moon. (Bhagavad Gita 10.21)
In the eleventh chapter of the Bhagavad Gita where Lord Krishna showed His Vishwaroopam form to Arjuna, the latter addresses Him twice as Vishnu Himself:
O all-pervading Vishnu, seeing You with Your many radiant colors touching the sky, Your gaping mouths, and Your great glowing eyes, my mind is perturbed by fear. I can no longer maintain my steadiness or equilibrium of mind. (Bhagavad Gita 11.24)
O Vishnu, I see You devouring all people from all sides with Your flaming mouths. Covering all the universe with Your effulgence, You are manifest with terrible, scorching rays.(Bhagavad Gita 11.30)
This clearly shows Krishna is Sriman Narayana Himself.
Krishna in Bhagavad Gita 10.23 says He is Shiva Himself:
Amongst the Rudras I am Shankara, of the Yakshas and Rakshasas I am the Lord of wealth (Kubera), of the Vasus I am Agni, and of mountains I am Meru. (Bhagavad Gita 10.23)
In the Bhagavad Gita 10.33, Krishna says:
Of letters I am the letter A, and among compound words I am the dual compound. I am also inexhaustible time, and of creators I am Brahma. (Bhagavad Gita 10.33)
This indicates clearly that the Trimurti are non-different from each other.
Also, Arjuna mentions both Brahma and Shiva while describing Krishna's Vishwaroopam form in the eleventh chapter:
Arjuna said: O Shree Krishna, I behold within your body all the gods and hosts of different beings. I see Brahma seated on the lotus flower; I see Shiva, all the sages, and the celestial serpents. (Bhagavad Gita 11.15)
Trinity is partially present but outside of Vishwaroop Darshan - Shankar as Rudra & Vishnu as Aditya - Vamana form. In Vishroop darshan only Lord Brahma is present according to non Vaishnava translation.
Shankar form -
रुद्राणां शङ्करश्चास्मि वित्तेशो यक्षरक्षसाम् | वसूनां पावकश्चास्मि मेरु: शिखरिणामहम् || BG 11.23||
Amongst the Rudras know me to be Shankar; amongst the demons I am Kuber. I am Agni amongst the Vasus and Meru amongst the mountains.
Aditya form -
आदित्यानामहं विष्णुर्ज्योतिषां रविरंशुमान् | मरीचिर्मरुतामस्मि नक्षत्राणामहं शशी || 21||
Amongst the twelve sons of Aditi I am Vishnu; amongst luminous objects I am the sun. Know me to be Marichi amongst the Maruts, and the moon amongst the stars in the night sky.
Now, in Vishwaroop form which was of KAl, Only Lord Brahman is witnessed.
पश्यामि देवांस्तव देव देहे सर्वांस्तथा भूतविशेषसङ्घान् | ब्रह्माणमीशं कमलासनस्थ- मृषींश्च सर्वानुरगांश्च दिव्यान् || 15||
O God, I see assembled all the gods and various beings in your body, Lord Brahman, seated on a lotus seat, and all the dazzling Rsish and heavenly serpents.
But Vaishnava scholars somehow put the name Lord Shiva in Vishwaroop Dharshan But it is not present in secular or unbiased work. Like see the commentary of Adi ShankarAchArya on the verse with translation, you won't find Shiva anywhere. -
I see all the Gods, 0 God, in thy body, as also hosts of various classes of beings : Brahma,. the Lord, seated on the lotus-seat, and all Rishis and heavenly serpents.
Commentary: Various classes of beings : both animate and inanimate, and of various forms. Brahma - the Four-faced, the Lord of creatures. He is seated in the centre of the Earth-Lotus, on the Meru which forms the cup or seed-vessel as it were of the Earth-Lotus. Rishis: such as Vasishtha. Serpents: such as Vasuki.