I posted about this elsewhere in Trek Tech, but for anyone who wants to build and accurate model of the "Tug" shuttles seen in Star Trek III and IV, here are photos of the actual filming miniature. Note that the coils at the back of the hull were intended to be tractor beam emitters. Bill George told me the ship was intended to be a tugboat that would help maneuver ships in and out of their berths. A fair amount of it is a kitbash. The nacelles and rear "deck" are the back end of an F-14 kit, and the inlet "scoops" are from F-16 jets. If you want to get it accurate, start with those as references to get the base proportions correct.
I posted these pics over on the Replica Prop Forum and already someone's started identifying exactly which kits were used in parts of it.
And if anybody wants to do a digital kitbash of this guy, there's decent, albeit low-poly, F-14 and F-16 models to be found here and here. I've made cleaned-up, higher-res versions of both the relevant parts, though I'm not sure if I'm going to do a full model of it. Might be fun, who knows.
Yeah, I can see the F16 intakes and the rear end of the F14. Very impressive level of detail on such a small model, those guys really knew their stuff.