As far as the pylon support structure, I'm mocking up something that I think could work. I'm using the interior shots from ST:TMP as inspiration and one thing I've noticed is that the TMP Enterprise is it seems that the pylons and neck support structure doesn't extend very far into the hull itself (at least not obviously anyway).
That's a very good point and from an in-universe perspective it makes perfect sense. It would call for some incredibly strong materials to work but hey; this is the future, right?
I'd be remiss at this point however if I didn't mention Cary L Brown's thread
, since it also deals with support structure (from a modern "common sense" viewpoint). It's a fascinating read!
Well, it might have been the hallway between the briefing room and transporter? In any case, the sets were changed between the 1st season and 2nd/3rd season, so that would factor in. But the "A" frame doors at the end of the radial hallway sections was the same in all cases.
Most of the changes were at the engineering end of the corridor - the section with the briefing room and transporter where pretty much unchanged (and unmoved) throughout the series run.
However, the stretch of corridor you mentioned is indeed the bit used by spock and McCoy in TIS:
However, the T-room side of the studio is not far from my own theory as to where the shuttlebay mockup was: (I'm using the 20' shuttle prop here)
One of the books (possibly "Making of Star Trek) mentions that the Engineering Room was used as the shuttlebay, but I just can't see how the shuttle prop could fit in there and leave all the space that we see in JTB, TIS etc.