I received the book a few days ago, I haven't started reading it yet but I did a quick check and I can say that the beginning is like the original film (no flashback and no Adam prologue), the sequence of SEN with the kids is similar to the script msycamore posted (so slightly longer than the original cut).

However, on the back of the book (the book is in Italian, whoever has the English version please check it!) it ends the description saying: the old story repeats itself. This time Adam of this future Eden is called THX 1138, while his beautiful room mate who will lead him into temptation is called LUH 3417.

In the same description it states that the story is set in the XXV century.

First published in Italy in March 1979 (I think that's when, in Italy, we saw THX for the first time, only after the success of Star Wars)