Music Composer v321a.BSC is a binscii file.  Inside that is "MC.v321a.SHK".

Music Composer v3.21a is the latest version of Music Composer the music sequence creating and editing progrom.  Version 3.21a fixes a couple of bugs in version 3.20.  Exported standard MIDI files were not formatted properly.  MIDI Record and MIDI Play radio buttons in the sequencer setup dialog did not work. These bugs have been fixed.

Clay