Sorry for the huge delay in responding, I wanted to check pynastran before saying any stupid thing... That looks a pretty extense module, but it is far away from my own area so I might not get the full idea. Anyway, if your module takes care of the reading/writing/parsing of nastran files, using it to make a FreeCAD import/exporter should be quite easy.
I would be curious to see the kind of output that your module produces (ie. what kind of data should be converted to/from FreeCAD objects). I have the impression that the nastran formats carry much more than only geometry, right? I'm not sure how far that goes, and, given the current abilities of FreeCAD, which don't extend much outside pure geometric work yet, how interesting it would be to import/export only geometric entities from FreeCAD to/from nastran file format?
Yorik van Havre
São Paulo, Brazil http://yorik.uncreated.net