And I just don't see the saucer being at all separable - it looks way too integrated to me, especially at the port and starboard edges, where it blends into the "sled" portion.
Could you please be more specific? According to this picture
and the bow view from the movie
all I can see is a saucer sitting "flat" on the "warp sled".
Neither does it look integrated with the Valiant study model
(notice the more protruding sphere below the nacelle cap and the rectangular, bulky looking shape of the warp engines).
The allusions I get from looking at the study model invoke images / analogies like that
Maybe, if someone "coated" the Grissom
with a layer of chrome on top of the "Apple White" such allusions would be more obvious.