I love the NX and NCC Excelsior but I have never been so disappointed in a refit as I was in the Enterprise B. I absolutely loved the unique look of Excelsior and the B upgrades literally eliminated 90% of what I loved about the ship.
I particularly love the secondary hull, at the front, and the Enterprise B modification was awful. It removed my favorite part.
As for the Greg Jein model that you sent a link to, be very careful NOT to use that as your guide for the shape of the secondary hull. He was way off on that. Compare his model to the filming model and you'll see what I mean. When his model was used in Voyager as Excelsior, intercut with the scenes from Star Trek 6, I was laughing that it was so easy to spot the new model. The original model was so different that it was obvious even at a glance.
If you're using reference pictures, I'd stick with the films above all else. I have a Lunar 41" Excelsior myself, and I started working on it in 1994. I shelved it when I realized my model building skills were just not up to par. I would sell it to someone if they felt they could do it justice. Otherwise I will just keep working on it in stages over the years. Also, I have a USS Grissom that is relatively to SCALE with this large Excelsior. Anyone doing a Star Trek 3 diorama could really use the Grissom to complete the set. If only they made a Bird Of Prey in this scale.