The concept painting Probert did around the time of TMP (which is what I'm thinking of, the one I thought Gerrold took to GR) seemed to have really long nacelles, or that was the impression (it was a mostly front view.)
I remember talking to Probert briefly back in 97 and 98 and I do recall him saying that except for the STARLOG SPECIAL EFFECTS mag (#3 or #4), pretty much everybody had always screwed up the captions and order of illustrations on his stuff (we were mainly grousing about THE ART OF STAR TREK, no surprise there!), but I didn't think this was part of that mess-up. Was pretty sure the GR rationale for shorter nacelles was to indicate the ship didn't need big nacelles because it was already so powerful (more of a conceptual notion than an aesthetic one IMO.)
EDIT ADDON: doesn't look like the links are working for the TNG stuff yet on his site. On the home page, there is one batch of e-d concepts that all have shortish nacelles though, so maybe you're right.
When i bought the model kit, I tried putting the nacelles on backwards just to make the ship longer and I thought it was tons better. Then again, I thought it looked better upside down and minus the dish entirely, too.
Maybe I better check Probert's site ... I remember it had lots of TNG stuff on it at some point ...