The double-post remark referred to this post
https://www.mobileread.com/forums/sho...&postcount=117
you will find DaleDe's answer just beneath
https://www.mobileread.com/forums/sho...&postcount=118
The PRC/Mobi book request-thread is here:
https://www.mobileread.com/forums/showthread.php?t=11648
But I would advise you to ask in the Calibre Conversion subforum
(
https://www.mobileread.com/forums/forumdisplay.php?f=235)
if someone could guide you step-by-step. Converting from epub to the new mobi format really isn't bitchwork. And you will be very proud of yourself if you accomplish it.