Genesis 5:4

RBT Translation:

And they are becoming the days of Red-one the back/behind the fathering of him,²⁰⁸ את-Seth eight hundred of a duplication, and he is fathering builders and built-ones.

RBT Paraphrase:

אחרי הולידו: Fathered from the Front

And they are the days of man ("Adam") behind the fathering of himself, self eternal Replacement ("Seth"), eight hundred fold, and he is fathering sons and daughters.

Julia Smith Literal 1876 Translation:
And the days of Adam after his begetting Seth shall be eight hundred years: and he shall beget sons and daughters.

LITV Translation:
And the days of Adam after he fathered Seth were eight hundred years. And he fathered sons and daughters.

Brenton Septuagint Translation:
And the days of Adam, which he lived after his begetting Seth, were seven hundred years; and he begot sons and daughters.

Footnotes

208

אחרי הולידו behind his fathering, behind the fathering of him. 

The word הולידו is an infinitive with the -ו  direct object suffix, "the fathering of him." It is also the verbal ending that marks the third-person masculine plural subject "they fathered" (Hiphil causative) but that doesn't fit anywhere in the context.

This form is found almost exclusively with אחרי in Genesis 5, and 11. So the two words together are trying to convey a certain meaning. After the fathering of him is overly complicated and unnecessary when a simple verb form could be used. The more mysterious thought provoking sense, Behind the fathering of him lends to the use of the infinitive with the adverb, instead of the more simple "after he fathered him."

Overall, it would seem there are many extra grammatical pieces to the structure that aren't necessary at all if the meaning was intended to be as basic as it has been made out to be.