Yes, Bhagwat gita's 18 chapters are said to be the body parts of Lord Shiva/Vishnu as said in the Padma Purana.:
śayālurasi dugdhābdhau bhagavankena hetunā |
udāsīna ivaiśvaryaṃ jagaṃti sthāpayanniva ||” (Padma Purana:UK:175:5).
“[Sri Lakshmi said.]: O revered one, You, despite being the sustainer of the world, you being indifferent (passive) towards your glory, are sleeping on this milky ocean, what’s the reason behind this?”.
nāhaṃ sumukhi nidrālurnijaṃ māheśvaraṃ vapuḥ |
dṛśā tatvānuvarttinyā paśyāmyaṃtarnimagnayā ||” (Padma Purana:UK:175:7).
“[Lord Vishnu said]: O you of beautiful face, I’m not sleeping, rather, by the vision which sees (follows) the truth, I am contemplating by being fixed (nimagna) in my true form of Lord Maheshvara (Lord Shiva)“.
bhavāneva hṛṣīkeśa dhyeyo’si yamināṃ sadā |
tasmāttvattaḥ paraṃ yattacchrotuṃ kautūhalaṃ hi me ||14
carācarāṇāṃ lokānāṃ karttā harttā svayaṃ prabhuḥ |
yathāsthitastato’nyatvaṃ yadi māṃ bodhayācyuta ||” (Padma Purana:UK:175:14-15).
“[Sri Lakshmi said.]: O Hrishikesha! You alone are always to be meditated upon by the self-controlled ones. Therefore, I have a great curiosity to hear from you, about that which is higher than you. O Achuta, tell me if there is something different from you who are the lord, the creator, and the destroyer of the worlds”.
māyāmayamidaṃ devi vapurme na tu tātvikam |
sṛṣṭisthityopasaṃhārakriyājālopabṛṃhitam || 16
ato’nyadātmanorūpaṃ dvaitādvaitavivarjitam |
bhāvābhāvavinirmuktamādyaṃtarahitaṃ priye ||17
śuddhasaṃvitprabhālābhaṃ parānaṃdaikasuṃdaram |
rūpamaiśvaramātmaikyagamyaṃ gītāsu kīrtitam ||” (Padma Purana:UK:175:16-18).
“[Lord Vishnu said]: O goddess (Lakshmi), this my body is illusory and not real, and is augmented with the mass of the acts of creation, maintenance and withdrawal. O dear one, the nature of the self is different form this. It is without duality and unity. It is free from existence and non-existence; and without beginning or end. It is pure consciousness, has acquired luster, is beautiful due to great joy, is the form of the Ishvara (lord), can be known only through the unity with the self, and this is what is told in the Gita”.
“ityākarṇya vaco devi devasyāmitatejasaḥ |
śaṃkamānā ha vākyeṣu parasparavirodhiṣu ||19
svayaṃ cetparamānaṃdamavāṅmanasagocaram |
kathaṃ gītā bodhayati iti me cchiṃdhi saṃśayam ||” (Padma Purana:UK:175:19-20).
“Hearing the words of him of an unlimited lustre, she having doubt to contradictory statement said: ‘If you are highest joy, and not known through speech and mind, then how does Gita make you known. Remove this doubt of me!'”.
“īśvara uvāca |
śriyaḥ śrutvā vacoyuktamitihāsapuraḥsaram |
ātmānugāminīṃ dṛṣṭiṃ gītāṃ bodhitavānprabhuḥ ||20
ahamātmā pareśāni parāparavibhedataḥ |
dvidhā tataḥ paraḥ sākṣī nirguṇo niṣkalaḥ śivaḥ ||21
aparaḥ paṃcavaktro’haṃ dvidhā tasyāpi saṃsthitiḥ |
śabdārthabhedato vācyo yathātmāhaṃ maheśvaraḥ ||22
gītānāṃ vākyarūpeṇa yannirucchidyate dṛḍhaḥ |
madīyapāśabaṃdho’yaṃ saṃsāraviṣayātmakaḥ ||23
yadābhyāsaparādhīnau paṃcavaktramaheśvarau |
iti tasya vacaḥ śrutvā gītāsāramahodadheḥ ||24
idaṃ paravibhedena budhyate bhavabhīrubhiḥ |
tamapṛcchadidaṃ lakṣmīraṃgapratyaṃgasaṃsthitam ||25
māhātmyaṃ setihāsaṃ ca sarvaṃ tasyai nyavedayat |26a” (Padma Purana:UK:175:20-26a).
“[Lord Shiva said]: Having heard the proper words of Lakshmi, the lord told her the Gita, the vision leading one towards the self, along with an historical account. “O great lordess, I am the ‘self’ differentiated in two ways, – as higher and lower. The higher is a witness, attributeless, partless, Shiva. As the lower one, I am ‘panchavaktra (of five faces)’ it also remains in two forms. I, Maheshvara, am the self, am to be explained through the distinction in words and meanings, as, through the words of the Gita, my strong noose of the nature of objects in the worldly existence, is completely cut off; since (realization of my two forms) ‘Panchavaktra’ and ‘Maheshvara’, are dependent on its study“. Hearing these words of him (which were) the great ocean of essence of the Gita, those afraid of the worldly existence know it through the difference between this and that. Lakshmi asked thus to him. He told her about the Mahatmayam (greatness) along with the corresponding historical accounts (stories) in its major and minor details.”.
“śṛṇu suśroṇi vakṣyāmi gītāsu sthitimātmanaḥ ||26
vaktrāṇi paṃca jānīhi paṃcādhyāyānanukramāt |
daśādhyāyā bhujāścaika udaraṃ dvau padāṃbuje ||27
evamaṣṭādaśādhyāyā vāṅmayī mūrtiraiśvarī |
vijñeyā jñānamātreṇa mahāpātakanāśinī ||28
atodhyāyaṃ tadardhaṃ vā ślokamarddhaṃ tadardhakam |
abhyasyati sumedhā yaḥ suśarmeva samucyate ||” ((Padma Purana:UK:175:26b-29).
“[Lord Vishnu said]: O you, beautiful lady, I’ll tell you about my firm existence in the Gita. The five chapters are the five faces in order. The (next) ten chapters are the (ten) hands; one is the belly, and the (remaining) two are the lotus like feets. Thus the eighteen chapters are the divine forms of words. It, destroying great sins, should be known through knowledge only. Therefore, he, the very intelligent one, who studies a chapter, or half of it, or a verse of a half-verse is liberated like ‘Susharma’”.
I hope this clarifies your queries.