Michael Palmers book, "Morgan 4/4 The First 75 Years" does give some insight into the model changes right up to 2008 which was the last of the Duratecs. After that it was the 1.6 Sigma engine.
He also gives quite detailed spec sheets for all the models from Series 1 to the final Duratec 1800's
However some of the information doesn't seem to stack up for example he doesn't show a track increase in 2000 ref Dave's post so I think it might be a bit generic to rely on for the detail we are seeking.
Mind you, when I was just getting into all this when I bought my car a year ago it did make very interesting reading.
