I think it's funny that so many people seem hung up on the fact that the shuttle mock-up is not 1:1 scale with the interior, considering that such int/ext discrepancies are common in movies and TV. On another board there was a discussion of the typical downscaling of set pieces to make them affordable and able to fit into soundstages.
The technical drawing efforts the I've seen, meant to reconcile the Shuttlecraft's interior and exterior, have shrunk the interior down to size. You lose a lot of headroom.
Blueprints for other things have gone in both directions:
The Space 1999 Eagle was done by Geoff Mandel at a length of 76 feet, resulting in an interior ceiling height of only 5.5 feet. Roberto Baldassari made his version 102 feet long, to fully contain the interior studio sets, but this put the eye-shaped cockpit windows far above the pilot seats.
Shane Johnson created a set drawings for the LIS Jupiter II, in keeping with the established size of the exterior, but he had to omit the entire lower deck. [He appended a nice lower floorplan with a note that it was for a proposed future version of the ship that would be much larger.]
Other, more recent Jupiter II plans have at least doubled the diameter of the saucer. This allows pretty much everything to fit inside, but the relationship between interior and exterior features gets thrown out of whack, especially on the top deck.
One of the most interesting and realistic reconciliations between interior sets and an exterior mockup (in this case, a backlot facade) is what Adam R. Jones did for the Bewitched house. He created a complete, working, buildable set of blueprints for this fictional house. It's at 1164.com.