Makes one wonder if the Kirk-era Enterprises had catwalks in the nacelles.
In TAS "One of Our Planets is Missing", Kirk and Spock take a bit of antimatter into what they call "the antimatter nacelle", using a catwalk in the center of a horizontal cylindrar volume. It wouldn't be that much of a stretch to claim that this is one of the warp nacelles, perhaps its very bow - and indeed Doug Drexler created his TOS ship cutaway drawing with this theory in mind, and it became sort of canonical when used in ENT "In a Mirror, Darkly"...
Whether we are to literally believe that one nacelle is matter, the other antimatter... I'd prefer not to. Jump-starting the drive from just one nacelle, rather than from Main Engineering, must be a special backup-of-backup scenario that might have its special procedures; perhaps only the starboard one is configured to receive the jumpstart dose of antimatter, and therefore enjoys this odd designation?
The FJ blueprints also had this same catwalk in the nacelle. Probably inspired by this very episode.
Also, it was Kirk and Scotty, not Spock.