I don't believe that anything you are looking for exists. I believe Ken Marschall was the technical advisor. My speculation is that what you saw in the movie was accomplished through detailed photo analysis combined with known dimensions of deck heights.
Bob is correct, there were no dimensional or decor plans drawn up for the Olympic Class as per say other vessels of the era, which for the most part but not always color and dimension mapped their interiors before outfitting. Almost all knowledge of the interior decor and woodcarving detail of the Olympic Class liners come from, like Bob said, photographic analysis combined with the known deck dimensions as well as written accounts and descriptions or in rare cases, the actual interior pieces in question are viewed if available. Unfortunately only the Olympic’s First Class interiors survived for inspection and as we know they differed from her sister in some ways, one example being the carpet and upholstery colorings, we can not be sure Titanic’s interiors were the same. Changes and additions were being made to the Titanic even as late as final outfitting, A-37 or the “Andrews Cabin” in the Aft Grand Staircase is just one of many examples of this. On that note, the Grand Staircase photographed and said to be on Titanic, and that has been subsequently used in all Titanic depictions in movies and artwork is actually that of Olympic. It is even rumored that the ornate Honor and Glory carvings were not finished in time on the Titanic and never installed and that there was just a simple oak panel with the clock in the center as in the Aft Grand Staircase. Because there are no known photographs of the Grand Staircase on Titanic so we can never be 100% sure of what it might actually have looked like.
Cameron and his production actually used plaster aswell as wood for their Grand Staircase. They went to the Swan Hotel (UK) where much of the Olympic's Grand Staircase has been re-built. Their collection even includes the Honour & Glory clock. On another thread in this topic there is "apparently" a man who has built his own Grand Staircase, you should talk to him.