@pdurrant, thank you!
Can you please tell me:
1) Can KindleUnpack extract only TOC? For the purpose of my project I don't need all raw files;
2) How can I get location of TOC entries in a mobi8 file? So
far, I can see that it only provides ordered TOC entry reference numbers. As a temporary solution to find percentage of a chapter is to calculated respective cumulative file sizes, but that's very rough.