The original shuttle for TOS was sponsored by the model company AMT so that they could get the rights to sell a model kit based on it. Shame the model is a totally inaccurate representation of the original and the bane of most Star Trek scale modelers - it ignores the curving upper details of the hull as well as the multi-level inset of the back end.
Back to the interwebs for more reference material. Phil Broad had drawn up a set of plans back in '04 which were originally over on cloudster.com, but sadly that site no longer exists - internet archive site waybackmachine to the rescue, at least for the majority of his drawings. Warped9, who posts on TrekBBS has also drawn up a very nice set of plans which formed the major basis for my version.
The basics are there, still some detail to add and a bit of tweaking with the shape but still an improvement on the AMT box...