walking through the net one day I've found
this- so I wrote

toc2nav as my contribution to Sigil epub3 functionality. It converts toc.ncx into epub3 nav toc and quide from opf into nav landmarks and adds it as nav.xhtml to Text files.
In the meantime I've modified DGSM a little.
DGSM 0.0.2 changes:
I've added loadNewBook to sigilActions as a preparation to write really clean importing alien formats. The idea is: when DGSM encounters noResource as required resource it gives the script the path to temporary data folder. The script could create this folder and leave something in it. On script departure Sigil checks the folder, do something with its contents -if any - and deletes it. At the moment by loadNewBook action Sigil opens the first epub book found there.
Got rid of some bugs, I think, I hope. It compiles on Windows but I have not done any tests.
Always use the latest DGSM with latest scripts package because I could have changed something

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The files are featured at the beginning of this thread.