So far I still haven't found anything that resembles a docking ring or hatch on either version of the Excelsior model. I find this strange, as the original ILM Enterprise-D had at least two rings on either side of the neck, in the recessed area behind the forward photon launcher, just like with the refit and the E-A. You can even see a tiny round hole where this ring is on the old AMT/ERTL model kit of the E-D, so it's not like they did away with the standard after the refit Connie's time.
If memory serves, there were some draft-quality schematics made several years back of the original filming model - I mean these things were BIG and highly detailed. They look like they were done with AutoCAD or some other similar vector-based app and could be printed on a large plotter. If someone knows where to find them again (I don't), we may be able to get a handle on some of Excelsior's surface features to get a good idea of scale. My poor ol' rusty brain can't remember when, where or who, but I definitely remember seeing them and they blew my mind.