[deback]

Yes, I'm sure. I just opened one of the .txt files I edited back in 2015 (when I did a bunch of these), and the ## is above the section heading, like this (it doesn't matter if there's a line space after the ## or not):

##
Chapter 1

blah, blah

I'm not sure if it will work if you enter the ## on the left of the section heading or not. I would have to experiment to see if it will work, and right now, I have no interest in doing any experiments.

Also, I've never heard of using dashes (or underlines?) under the section headings, so I can't tell you if this will work or not without testing it.

Each ## tells Calibre conversion to place everything below the ## into a separate html file. The ## will not be included in the converted file.