Hi Quentin,
I work at the South African Astronomical observatory, and we have just started building a Morgan, however we would like to modify some of the printed parts. (also a few of them are not watertight).
Could we get some copies of the autocad or NX design files?
The source files are on the git repository. It is designed in OpenSCAD.
You can find the Inventor files on the reprap wiki, done by Robert Kuhlmann. It is quite an accurate reproduction of the original, and should be helpful to you.