The scale issue wasn't to hard to figure out when you look at this stuff... the early ship would be barely large enough for a crew of 50 (as I recall the early crew estimates from the summer of 1964 were for 25). The 203 lives sounds more like a mistake in thinking that doubling the size would give you four times the square footage and forgetting that the number of decks is also doubled.You mean sort of like this?
That's it exactly. There was a preliminary Jeffries sketch along those lines, part of a series of 3 sketches where he was trying to decide what the final scale should be. The alcove graphic is similar but not completely identical to this.
But the date of the final plans is known... November 7, 1964. The date is not debatable, Jefferies wrote 11-7-64 on them (which is where that date comes from). Every thing else (that I know of) where the ship was in some form of size transition is from October 1964 and earlier. Solving those issues had to be done first before going out and hiring Datin (who later would hire Volmer Jensen's shop for the 11 foot model).
We know that Roddenberry saw the final assembly of the model about two weeks after Datin had started it. That Roddenberry wanted more details on it and the inclusion of windows (up to that point the purpose of the 11 foot model was for the bridge zoom in which was supposed to show the scale of the Enterprise, so the bridge was to be the audiences' reference point... in Jefferies view). Jefferies drew windows directly on the original plans for Datin to use in detailing the model. When Roddenberry was happy (and the production of the models way behind schedule) Datin was given the okay to start the 11 foot model (December 8, 1964).
The final (heavily detailed) 33 inch model was given to the production on December 14, 1964. That date is based on two data points... it was noted by Datin and the photos of the event show the background which matches with the dates on the clapboards from the dailies.

Don't get me wrong... I believe that you not only recall that a magazine said something long those lines, I believe that you are accurately conveying the information. But I've found that most of the magazine references I've seen from the 70's, 80's and 90's have erroneous data. And even people who were there have made mistakes in recalling past events which don't match with the larger (and growing) collection of facts.