The devata of Rigveda tenth mandala 47 and 48 suktas (hymns) is Indra Vaikuntha. This is not Vishnu but one of the incarnations of Lord Indra. He is named as Vaikuntha because of his mother Vikuntha, daughter of Prajapati.
There is a text called Bṛhaddevatā which is written by Sage Shaunaka. This text contains the details of the deities worshipped in hymns of Rigveda. It also gives the background stories of composition of the mantras.
There is explanation given for these hymns.
In this answer, the deeds of Indra was described.
There was an Āsuri, daughter of Prajāpati, Vikunthā by name. She, desiring a son like Indra, performed very severe austerities. She then obtained from Prajāti her desires (in the form of) various boons. And Indra himself was born of her, as he wished to slay the Daityas and Danavas. Once he was engaged in battle with the Danavas.
Of them he slew nine nineties and seven groups of seven. Having shattered with the might of his arm the citadels of gold, silver, and iron, (and) having slain all (of them) in their respective spheres (yathāsthānam), as arrayed on earth and the other (two worlds). On earth he exterminated both the Kālakeyas and the race of Puloma, the archer, and in heaven the notorious (tan) offspring of Prahlada.
My question is - Was deed of Indra in demolishing the citadels of gold, silver, and iron, of Danavas, source for the story of destruction of 3 cities of Tripurasura by Shiva?