[nickredding]

I have just confirmed that if you take a mobi created by kindlegen2 with both mobi7 and mobi8 parts, you can copy the RESC, FONT and image records from the mobi7 part over to the mobi 8 part and delete the mobi7 part (you have to update last content record and the FCIS and FLIS indexes in the mobi8 part to account for the additional mobi8 records). The resulting mobi8 file works fine on the kindle previewer and my Kindle Fire. I also checked an unencrypted file that uses fonts as well as images, and again no problem.

This is good news because it means I can generate mobi8 files without bothering with the mobi7 part that kindlegen includes (I'm looking at this from the point of view of creating a calibre writer module for KF8). I spent two days trying to figure out the interaction between the mobi7 and mobi8 parts (when both are present). There IS some interaction but it is quite opaque, and if you get it wrong either the file will not load or it will fall back to the mobi7 part even when you put it on a KF8 device (previewer or Fire).

I personally don't see much use for combined mobi7/mobi8 files. Eventually there will be calibre input and output modules for KF8 so if you want a mobi7 from a mobi8 you'll be able to convert (calibre will just throw away most of the KF8 styling for the mobi7 output which is what kindlegen2 does).

For anyone who is interested I have attached the python script I used to remove the mobi7 part (I started with the latest mobi_unpack.py so acknowledgements to the creators of that).