Prajapati gave his daughter Surya Savitri to King Soma and made a thousand verses for the wedding. The gods each claimed it and agreed to race, from Agni the lord of the house to the sun. Agni led; the Ashvins said 'Give way, we two will win this'; he agreed for a share. So with Ushas. To Indra they dared say only 'We will win this, generous one'; he too took a share. The Ashvins won, so the litany is the Ashvina, with sections for Agni, Ushas and Indra. Agni ran with mules and burned their wombs; Ushas with ruddy cows, hence the red of dawn; Indra with horses, whose neighing marks lordship; the Ashvins with asses, whose speed was spent, though they kept their seed.
The stallion ass of the twins won 'that thousand' in the race (1.116.2). The Daughter of the Sun mounted their car, which reached the goal first, and all the gods assented in their hearts (1.116.17); she chose their car (1.117.13); delighting in them she ascended it (1.118.5); the maid of noble birth who came for friendship elected them as husbands (1.119.5).
What is different here:
The prize is the bride herself, who chooses the twins as husbands; no Soma, no bargaining with other gods.
Soma woos Surya; the two Ashvins are groomsmen and Agni leads the train. Yet verse 14 says that when the Ashvins came on their three-wheeled chariot as wooers all the gods agreed and Pushan chose them as fathers, and verse 15 asks where one of their chariot wheels was then.
What is different here:
Bridegroom is Soma, the twins his groomsmen, with a trace of the older version in which they are suitors; adds the riddle of the missing wheel.
Sources: Rigveda Brahmanas: the Aitareya and Kausitaki Brahmanas, tr. A. B. Keith (1920); Hymns of the Rigveda, tr. R. T. H. Griffith (1896), hymns read for the Vedic layer