Do not such similarities (just mentioned, between Gen 9:18-29 and Gen 2-3) suggest contrivance by the author, rather than faithfulness to some events?

How likely is it that the events were designed by God to match each other? This might turn out to be a general problem: when the carefully contrived details of a narrative seem best explained by choices made by the author, that would certainly seem to indicate that the narrative was literally contrived, i.e., fictional and mythic, rather than actual. I do not believe we have seen many other examples so far; still, the symmetrical structure of the weeks and months given in the Flood, discussed above (q.v.), are another example. Yet my approach in this case is slightly different. We need only observe that the events in both cases here flow naturally, and that adequately explains their similarity. It was inevitable that Adam, and Noah, would sin; after that happened, they would (at some point, in the case of Noah) be caught, and the nakedness in both case just happens to be integral to the story. That a mixture of merciful blessing and just punishment follows is perfectly natural. Now, it is possible that, out of the sins of Noah, this one was selected because it involved his nakedness that resulted from consuming the fruit of the vine, this in turn because it recapitulates the symbology of the Fall (the fruit of temptation and the nakedness before God that follows sin). It is also possible that God permitted Ham to be tempted to gaze upon his father and mock him to his brothers, because this prophetic lesson would result.