"Godolphin" is an old Cornish name. Godolphin is a parish in Cornwall, the most southwestern county in the United Kingdom. There was a character named "Lord of Godolphin" in J. Swift's Gulliver's Travels. There's a Godolphin Street in London.
However, a couple years ago HyperArts received an email from Ellen Godolphin Bernstein, which likely explains the source of the name. Ellen wrote:
- Tom Godolphin was my father-in-law. He was on the English faculty at Cornell when Pynchon was a student there. You can read a little about him in an essay by John McPhee called I think A room full of Hovings. He was killed in an automobile accident in the early 1960s.
Other speculations before the above:
From Thomas Pynchon: The Art of Illusion:
- "A final iconographic detail [...] may be intended by the author's having Victoria often attended by Hugh or Evan Godolphin. Their surname puns on the name of the aquatic mammal that attends the goddess in certain ancient representations, e.g., the Aphrodite of Cyrene." 
- "Rainer Maria Rilke's poem Die Geburt des Venus concludes, after the goddess steps ashore, with the washing-up of a dead dolphin, "tod, rot, und offen." 
Also, Hu Gadarn, the Welsh god, is mentioned often in The White Goddess, to wit:
- "Hu Gadarn, 'Hu the Mighty', who has been identified with the ancient Channel Island god Hou, was the Menes, or Palamedes, of the Cymry and taught them ploughing-- 'in the region where Constantinople now stands'- music and song." 
- "The Cymry, whom we think of as the real Welsh, and from whom the proud court-bards were recruited, were a tribal aristocracy of Brythonic origin holding down a serf-class that was a mixture of Goidels, Brythons, Bronze Age and New Stone Age peoples and Aboriginals; they had invaded Wales from the North of Englad in the fifth century A.D." 
- "the hero who led the Cymry into Britain from Taprobane (Ceylon)" 
- Cowart, David, Thomas Pynchon: The Art of Illusion, Southern Illinois University Press, 1980, p 19
- Ibid. p.138, fn.5
- Graves, Robert, The White Goddess, Farrar, Straus and Giroux, New York, 1948, p. 88
- Ibid. p. 19
- Ibid. p. 145