Well, first of all... the supports are solid wood, and would most likely hold my weight (210 lb.) without any noticeable sag. The area where they connect to the secondary hull was so re-enforced that all they do is slide into the openings and fit perfectly snug. The front third of the nacelles were originally solid wood as well (later drilled out for the dome motors), and the supports are held in place with two 3.5 inch screws for each nacelle.
The thing is, not only were the supports over engineered for the task of supporting the nacelles, for most of the life of the 11 foot model, the stresses on the supports have been fully reversed as the model was hanging from it's nacelles.
The major difference in the placement of the nacelles most likely happened when Datin was test fitting the 33 inch model's components. Before adding any of the details to the parts, he most likely noted that the nacelles worked better when swapped. In the following diagram I show the Enterprise as planned by Jefferies, and the Enterprise assembled by Datin (which only required a switching of the port and starboard nacelles, and a shortening of the supports for them to be at the same height as the original plans).
That not only puts the nacelles in almost the exact position that they are in on both the 33 inch and 11 foot models, it also almost exactly matches the connection point of the supports on both models as well.
I'm sure that few people would be interested in this, but I'm mapping out all the pieces of wood used to make the secondary hull (inside and out) and where holes were drilled/cut to allow for lighting of the model. I'll be outlining that stuff after I finish with my notes on the nacelles.