The last time I checked, the disclaimer included with the last set of assimsoft plugins for MS3D said they were open source, intended for any enhancements people may feel were necessary. At the very least, I do know they're open source.
Thing is, I don't know if it's possible to use the open source code for the SFC, and perhaps even BC plugins, from MS3D, and adapt them to 3D Studio Max. The SDK for MAX is readily available for download.