And the movement of Kirk, Spock and McCoy at the beginning of "Journey to Babel" suggests passage trough two circular corridor segments (parallel to one another, same pieces of the studio set) that must have a different radius unless we assume these two circular corridors to connect with one another and form a larger corridor with the basic shape of a "?" (which, IMHO, would look extremely odd and out of place in the saucer hull).
Out of place maybe,but not without precedent (well, in the same episode anyway). When Kirk has his fight with the Andorian, there is an odd cut near the end when Kirk delivers his final knockout knee-to-the-head:
See that? The corridor curves clockwise in relation to Kirk from one shot, but anticlockwise from the other shot! In other words, we end up with a corridor shaped (more or less) like this:
And this is in "Deck 5, near my (Kirk's) quarters!" Where on earth might this perculiar corridor segment fit?
As for Kirk, Spock & McCoy's trip through the hallways at the start of the episode, I always assumed that the second corridor sequence was some distance away from the first, probably inthe secondary hull as they made their way towards the Hangar Deck. Certainly they do pass a sign directing them back toward the "Transporter Section" which (as you've suggested elsewhere) is likely to be in the same hull as the Shuttlebay.