So another update about the whole N64 music thing... I've been through the tracks in the trial, and it seems the old save room theme is not present. The track mentioned earlier is definitely the end credits theme (edited my post to reflect that). However, some N64 themes do exist, and those have been uploaded in the past. Of course, the uploader didn't say where they came from... they're from the trial disc! I posted one of the tracks myself for clarity:
This is the track that plays in the train scenario of the N64 version. It can be heard clear as day in the live E3 footage posted earlier. There's a vaguely similar track in the final game, but this particular one is not.
So there you have it!