The distance between the CMS header and the CMSN
header appears to be
 much larger than 800 bytes--the first, for example is about 4K . The
 next CMS file name header follows about 80 bytes later. 
Later versions of the filesystem would be more likely to use 2k or 4k
blocks.
  I don't see any indication of file or record
lengths in the header,
 which is troubling.  The first block has the following (ASCII
 version) 
The FST contents would be the filesystem metadata, wherever that has
landed.
De