I really am humbled! Thank you all!
Given the honourable status this model has unexpectedly achieved, I feel obliged to 'fess up' on some of the later stages of construction:
1. Spine rod. I left a small length of dowel visible at the front with a longer length at the tail. Turns out would've been better to paper right up to the front of the rod and leave a longer tail end. This wasn't an issue as I was able to wrap a length of paper as a 'tail pipe' to ensure a good solid connection inside the propulsion section.
2. Joining the hemispheres. I was in two minds as to the best way to do this. I had originally left a 'tab' around the bottom edge of the top hemisphere (should be visible on photos) but I ended up removing it and making a clean edge. This was after looking carefully at other build threads! I plumped for it being safer to apply an inner rim to the bottom hemisphere, so that it ended up flush with the edge. Note I applied it with plenty of glue so that there was no need to pinch tight and risk the tabs from the pod bay doors becoming visible on the outer hull - that way disaster lies! Having done that, I then applied a replacement tab to the inside edge of the top hemisphere, which made a really good connection with that hidden inner rim when the two halves came together. This also helped preserve the recessed darker band round the 'equator'. I was really happy with the outcome.
3. That neck join. My heart was in my mouth when I placed the sphere on the neck. It was mis-shapen and too baggy! That first photo I posted of the sphere on the neck in front of the fireplace - you'll see that the bottom left of the sphere shrinks back from the neck join - and that's after I applied the fix! I was gutted! Despite careful cutting and alignment of panels, it came up short! I attempted a fix by creating an additional 'collar' to slide over the end of the neck. I made it in exactly the same way as the neck end, attaching two equal strips top and bottom so that they could slide snugly over the end of the neck. The new collar was then glued on to the tabs inside the hole in the sphere, and the result was remarkably effective by way of fixing what could have been a very messy situation. I think fitting the collar helped fill out the shape of the sphere correctly, reducing the size of the gap as a result.
Here endeth the confession!