That's the beauty of it - there is no need for Finney to comfortably fit inside the pod if it is an ejectable automated device.
Basically, the pod would be a glorified spacesuit, a "hardsuit" typical of 1950s science fiction and fact. Only, this particular pod would be a modification, a probe to be launched from the hardsuit deployment chute. One would still access it the very same way, by crawling into the horizontal chute and into the stem part of the mushroom-shaped device. No room for helping hands there - the perfect vehicle for Finney's nefarious plan...
That the TOS-R folks didn't opt to alter the shape or dimensions of the starship or its random surface featurettes strikes me as particularly elegant.