I'd find it odd the engines were being built on site with the rest of the ship. I'd think an entirely different manufacturer would've made the engines.
You'd have to remove some sections to get at the connections and to install bits and pieces that are specific to this one ship at the yard that's what we could be looking at.
Or it could simply be that the yard here is tasked with applying the surface finish, all those plates of unobtainium, on all the components that have been manufactured elsewhere sans plating. Once that's done, all the things could be shipped to various parts of the globe again, to receive their final innards. And then the whole kit 'n kaboodle is launched to space, separately, component by component, and assembled there.
Or then the surface plating is done as the very first stage of construction, on this yard, and the components are then internally furnished. You know, how they used to build ships in the past.
I mean, we'll probably never see any further shots on the actual construction of the big bad lady. The first time we see her in the movie will be when she already floats in space. How she got there is and will remain anybody's guess.
As for "back or front", I refrain from voting - but I remain convinced that the fins will be close to the back of the nacelles, because that's the definition of cool. Impressions to the contrary must be optical illusions.
If it's a nacelle, then shit, this a huge f***ing ship!
Or then Star Fleet Division prefers imported labor from Dwarvia Minor.
But the TOS ship could use some scaling up, to give the saucer at least two full-height decks and stuff. TMP ship, likewise, of course, to fit in the Rec Deck without applying technology proprietary to Time Lords. Still, 3x scaleup is a bit excessive...
Timo Saloniemi