I like what they did with the necks, the lines flow better than in the original drawing. I think the pylons and nacelle configuration is a bit too Sovereign, though. I think I'd like to see them moved in and up, like the original drawing. I do like the nacelles themselves, though, they look sleeker than the drawing.
the clay model does look impressive the neck has been shortened (it looked weird in the original), and the nacelles look sleeker
as for the saucer, the J's was circular, while the E's was ovoid... the clay model is more round than the E's, and a little less forward, so that's part of the evolution i'm guessing