It works!
It looks like Calibre is the way to go, since the original HTM comes from BD. Simply dragging that into Calibre generates h2 tags where there was something else in BD.
I used this to create the TOC and page breaks:
Code:
//h:h2[re:test(@class, "title", "i")]
My old process of RTF>BD>SIGIL>CALIBRE is now shortened because I can skip the Sigil part where I created page breaks and adjusted font stuff. Calibre can do all that.
I'm sure Sigil will be handy for any later tweaks I might need.
This does not directly solve the LRF conversion problem, but I have the original BD files which can quickly put out HTM for Calibre conversion.
Not to mention I discovered a type of TOC I didn't know existed.
Many thanks to all!