Allusion in the Modern Novel

I was reading Marilynne Robinson's novel Gilead tonight, and in one passage the narrator describes himself and a friend as boys spending large parts of the summer walking around on stilts. At one point, he says (p. 38), 'Giants in the earth we were, mighty men of valor.' That sounded familiar to me as a description of the Nephilim in Genesis (6:4), so I checked some English translations. Here are a few samples (from
here):

The Nephilim were on the earth in those days—and also afterward—when the sons of God went to the daughters of men and had children by them. They were the heroes of old, men of renown. (NIV)

The Nephilim were on the earth in those days, and also afterward, when the sons of God came in to the daughters of men, and they bore children to them. Those were the mighty men who were of old, men of renown. (NASB)

The Nephilim were on the earth in those days, and also afterward, when the sons of God came in to the daughters of man and they bore children to them. These were the mighty men who were of old, the men of renown. (ESV)

None of these uses the translation 'giants', preserving the word 'Nephilim' instead, but I found a couple examples that do:

There were giants in the earth in those days; and also after that, when the sons of God came in unto the daughters of men, and they bare children to them, the same became mighty men which were of old, men of renown. (KJV)

There were giants on the earth in those days, and also afterward, when the sons of God came in to the daughters of men and they bore children to them. Those were the mighty men who were of old, men of renown. (NKJV)

I suspect that the KJV is the source for the reference, since it seems to me to be the most popular translation for literary use (and, in fact, it was used to quote Job 1:21 on p. 30), but, just in case, there is a parallel in the Septuagint as well:

οἱ δὲ γίγαντες ἦσαν ἐπὶ τῆς γῆς ἐν ταῖς ἡμέραις ἐκείναις καὶ μετ ἐκεῖνο ὡς ἂν εἰσεπορεύοντο οἱ υἱοὶ τοῦ θεοῦ πρὸς τὰς θυγατέρας τῶν ἀνθρώπων καὶ ἐγεννῶσαν ἑαυτοῖς ἐκεῖνοι ἦσαν οἱ γίγαντες οἱ ἀπ αἰῶνος οἱ ἄνθρωποι οἱ ὀνομαστοί