OTOH, the sled, too, has a glowing aft fixture - the square thing just below the pod, and off to starboard. That's the color of the shuttle glow, too, FWIW. Probably not an engine there. But possibly an engine in the pod. That is, unless it's just a pair of lamps for illuminating final approach to a docking port. Or a pair of glowing sensors for achieving the same.
The general issue would seem to be that the pod doesn't look capable of independent ops much. The docking port is supposed to work so that it absolutely requires a mothership for the opening of the doors, say. We can postulate a side door, much as in the smaller version of the pod Probert sketched for use as an
Enterprise auxiliary, but what the shooting model actually has there is just a pair of side windows...
Top-mounting would rule out it using those docking ports under the saucer, inside those hatches.
But nothing can dock there anyway, not without a veritable trunk as the docking adapter.
Nacelle placement above or below wouldn't affect docking with the side doors, which in any case make the most sense because the engineers would want vertical walls for vertical doors so that they could have horizontal floors... But the real damning fault of the design for the purposes of docking with the sled attached is that there's this stern overhang, this protruding of the nacelles several meters farther back than the rear docking tube.
The sled looks fast, very fast. Vulcan to Earth in about a half day, or somewhere around 1 ly/hr.
We can always argue V'Ger was approaching from the direction of Vulcan (and today, we want to, because we "know" 40 Eridani sits nicely between Earth and Klingon territory), so it would be Kirk's ship doing the traveling, not Spock's sled.
We can't tell where Spock was hoping to go in that courier. Was he already on his way to Earth even though Kirk's hastening of the launch meant Spock would be way late? Or did he only launch after learning that Kirk had launched, and was setting up a rendezvous somewhere en route? Did Spock have prescient powers here, for his usual Vulcan reasons or thanks to V'Ger somehow?
How did the wormhole figure in that? Did it give Kirk a boost, or stop him in his tracks, or fling him sideways? For all we know, the
Enterprise was basically gliding past Vulcan when Spock boarded.
...Or had already passed Vulcan and thus would catch up with Spock who was independently hurrying towards V'Ger, aboard a contraption he had put together out of an expendable travel pod and a stolen pair of warp engines intended for cargo hauling or whatnot, so that nobody but him would need lose his or her life in the adventure? Chekov does have difficulty identifying the very configuration of the approaching vessel, even if Uhura can tell it has a Federation shuttle transponder onboard. (Sure, both parts also have the same Vulcan lettering, supposedly saying "Surak" in Vulcaneseian - something Spock would be unlikely to paint on the side of a makeshift kamikaze vessel!)
Timo Saloniemi