*.mdl files are NOT designed for reverse engineering.
However, *.msh files [mesh] are made for reverse engineering. Orbiter Space Flight Simulator uses meshes for its visual models.
*.msh files can easily be imported to Gmax by simply using the proper Maxscipt and running that scipt.
With the same Maxscript, you are also able to export it back to a *.msh file.
Just as a note, Orbiter Space Flight Simulator can be found at
http://www.medphys.ucl.ac.uk/~martins/orbit/orbit.htmlSo basically, whe are lucky that Microsoft never used the *.msh files for the visual models. It would have left our freeware addons volnurable to pirates who steal our work.
With the *.mdl files, it makes it almost impossible for the pirates to steal our work and sell it off without our permission.