Hi guys! Regarding the Excalibur I consider her to be a variant which the scene you posted (of the reused Yesterday's Enterprise footage) to be just saving money by the producers of the show for that one scene. My reasoning is that the studio model was altered at this time to be the Excalibur for that fleet scene and half the decals were still present when the model went to auction. Since the model was altered for the Zhukov in data's day (albeit with an incorrect name and NCC number), I assume that all Ambassador class ships which made onscreen appearances from that point onward were of the variant design. While I want to believe that Starfleet put them all in drydock and updated them at some point before TNG time, the idea for me that Starfleet repositioned the neck and nacelles as you described seems unrealistic which is why I lean to the theory of two batches built in two different configurations.