A found a Pascal interface on those disk images. It could be useful for someone trying to document the file system. I attached it to this post.
Here's a little excerpt from it:
DirNBlocks = 4;
TYPE
{$IFC MONITOR}
IORsltWd = (INoError, IBadBlock, IBadUnit, IBadMode, ITimeOut,
ILostUnit, ILostFile, IBadTitle, INoRoom, INoUnit,
INoFile, IDupFile, INotClosed, INotOpen, IBadFormat,
IStrgOvfl, IWrProt, IDevError, INoDirSpace);