Today, after a lot of work, I finally have a reconstructed, working disk from the AF117a disk with filesystem errors caused by partly-overwriting it.
To do this, I used my Amiga 1200 and WinUAE running Workbench 3.1, the Amiga tools TSGui, DiskMon Tools, LZX 1.21 and 1.20 Registered versions, DiskSalv and TrackEd, Cygnus Hex Editor for Windows and ChkSum, CopyDate and DirDate command line utilities for DOS, together with replacement files from an AF103b disk image from AMR and Fiasco 2.22 main and English docs archives from Aminet.
Thanks to both Toni Wilen
and Thomas Rapp
for their suggestions and help with this, which put me on the right path!