Downloaded SWIG from here. Added directory containing swig.exe to my path, added PYTHON_LIB and PYTHON_INCLUDE env variables.
Also switched to 64-bit compilation (see original post).
As I don't have a debug version of python27.lib, I switched both Dragonfly (inc all submodules) and PyDragonfly to the Release version. I presume there was another way to specify the non-debug library to link to but this so far seems to have worked and was easy.
Install ctypeslib and ctypesgen, and define CTYPESGEN environment variable as path to directory containing ctypesgen.py. Actually, I'm not sure if ctypeslib is needed - it was under linux, I think, which is why I tried that first.
Experience report for building Dragonfly on a Windows 7 64-bit with Visual Studio Express 2013 (a free version):
[EDIT - all is now working. I have edited the above to show the steps undertaken.]