I remember in some episodes they would make a distinction like "engineering, on the lower levels"
From the Enemy Within
SCOTT: Mister Scott, sir, on the lower level of the Engineering deck. I've found a new trouble with the transporter.
or "engineering, on or near deck c", etc.
You're perhaps thinking of this line from Court Martial
KIRK; Localise that.
SPOCK: B deck, in or near Engineering.
KIRK: Seal off B deck, sections 18Y through 23D.
Incidentally, other than reference to a "Weapons locker on H Deck" in Conscience of the King
at no other point in TOS are decks referred to by letter. Perhaps "B Deck" is the lower level of the engineering section?
I figured Kirk and crew would check with the bridge while in transit on the turbolift which one to go to
The scene in Is There In Truth No Beauty
that I was thinking of occurs just after Marvick calls the bridge and rants to Kirk, who simply call for "security to Engineering". I suppose Uhura (professional that she is) could have relayed further directions to the Redshirts...
As for squeezing in those long curved corridors, it's just a matter of building what we actually see, not what we know is there. The corridor in Naked Time
need not be a circle, thanks to the following camera cut:
If you want to include the view from court Martial
(and make the corridor layout as symmetrical as possible) it might be arranged thus:
Perhaps not as elegant as a circular corridor, but it'll certainly fit in the Secondary Hull!
I imagine that the S1 Engine Room is near the top of the Secondary Hull. The Engine Room seen on Ultimate Computer
I see in the middle. The long circular corridor can be made to fit by pivotting on the radial corridor by 12 degrees:
Here I've overlaid a block colour diagram on Casimiro's Secondary Hull, the blue sections are the ones which have moved:
The pivot is not that severe and could easily have been what we saw in the episode:
<click for larger image>
Anyway, that's enough page wasted! I'm sure you get the general idea. It's a solution, anyway