Just FYI, GSchnitzer replied to a question
in the topic Doomsday Machine Question-What Does Decker Exclaim?
over in the Star Trek TV Series > Star Trek - Original Series topic about how the shooting script describes the Constellation. Here's his reply:
...There's not much there there we don't already know.
"Scene 8 INT. ENTERPRISE BRIDGE - ON VIEWSCREEN
SHOOTING PAST Sulu on the left, holding part of naviga-
tor in the right. Showing an Enterprise-class starship
seen small at first, but growing in perspective as the
Enterprise approaches it, till it fills most of the
viewscreen. We see that it is the Constellation, sitting
dead in space, with several large, neat holes punched in
the warp-drive pods, obviously a derelict, She is canted
at an odd angle and looks somehow grotesque in her help-
Other scenes have even less content. Here's Scene 11, when we return from the opening credits:
Scene 11 EXT. SPACE - FULL SHOT - CONSTELLATION
The wrecked Constellation floating dead in space, canted
to one side; the holes in the power nacelles are clearly
So it looks like the took an "Enterprise-class" starship model and poked some large holes in it and made it look obviously derelict. And script-wise, that's about all they had to work with.
Which pretty conclusively indicates that the ship was supposed to be the same class
as the Enterprise, not some other model, despite the registry or the differences in the AMT kit.