Pdurrant has graciously consented to provide some tutorials on using Amazon's Kindlegen to create true MOBI files from an unziped Sigil file.
Start a thread in an appropriate forum, and point me to it.
Since, at least to me, this is the technical ePup forum I have taken the liberty of starting a thread here. If I'm wrong I'm sure I'll be so informed.
Many thanks, Paul.