OK, if I remember correctly from old blueprints, the base of the neck along the spine of the secondary hull used to be where the deuterium tanks were. This are is where I saw the core(s) eject from the area where the neck blends into the secondary hull.
To me, I think because of the timeline change, the way Federation ships get to warp is much different. Someone up thread mentioned it, I think the nacelles are now much more self contained units then we have seen previously and the engineering deck now acts as a monitoring room making sure the nacelles get what they need to run and keep them balanced - hence the piping and various controls.
To me the nacelle front caps (the former bussard collectors) reminded me a lot of the swirling lights in the warp core in ST:TMP, indicating to me anyway that more is going on in there then we have previously seen. I think also the additional size/girth also supports this.