Okay, so I rechecked my 3D model.
When I drew up my initial schematics my design measured out at 8.0549 metres L.O.A. or 26.426837 ft. (26'-5 1/8"). The 3D model forced me to revise the size (due to a small error I had in my drawings) so the present measurement is 8.299679 metres L.O.A. or 27.22992 ft. (27'-2 3/4").
So my shuttlecraft went up 9 5/8" in length. And that allows for a 5'-9" interior ceiling. The length of the interior cabin (nose to aft cabin wall) is 19.276678 ft. (or 19'-3 5/16").
Removing the nacelles and aft landing strut subtracts about 2.5 ft. from the overall length, so you have a main hull under 25 ft. (about 24’-8”).
Close enough?
So you're finding that "The Galileo Seven" episode interior as seen, with headroom over Spock's six feet, and a machinery compartment under the floor, yields a bigger exterior than we can accept. That figures. They designed the exterior to be a vehicle you sit in, and then built the interior without regard for that.
Also, the difference between 27.22992 and 27.23 is less than a 1000th of an inch. That is literally a coat of paint. So I'd go with some sensible rounding.
