I'd originally planned to build the ship as seen in TMP. However, due to a few quirks in the kit and few creative fixes on my part, I've redirected her place in the time line.
Now, the model represents the Enterprise as she may have appeared after TWOK. Starfleet being Starfleet didn't want to expend resources on another full ship refit on a ship that was already past her fifteenth year of service. Even worse, she would soon be supplanted by new technology that wouldn't work with the core Constitution class frame still lurking under the modified appearance that the Enterprise class would take on from the design board to the shipyard.
Due to her age and the damage inflicted on her hull by the pirated USS Reliant, she does not appear to be showroom new. The damage is repaired and she is fully space-worthy, but there are scars. Rough welds in her hull in places.. Evidence of radiation damage on the edge of some hull plates and so forth show that she has fought and survived where others have not.
A new generation of RCS thruster has been added to the ship. These required some additional structural reinforcement and larger hazard zones than the previous thrusters. The Mark V thrusters are easily recognized on a ship due to the copper-colored hull reinforcements around them.
DSCF1889 by Wulfgar28, on Flickr
With luck, I will have the decals on the engineering hull completed entirely this evening.
DSCF1890 by Wulfgar28, on Flickr