Two great tips via The Building Coder today.  Firstly, the updated Revit SDK is available for download from here.  Here are some links:

Revit 2014 SDK (Update April 24, 2013) (exe – 217899Kb)
Revit 2013 SDK (Update April 11, 2012) (exe – 161112Kb)
Revit 2012 SDK (Update June 22, 2011) (exe – 151105Kb)

Secondly, did you realise that Revit 2014 comes with a tool to convert gbXML data into a dwfx file?    Look in your Revit program folder for a file called gbXML2dwfx.exe