I'm preprocessing anyway. Not to worry, I think I've got it covered, I'm converting the rtf to epub with Calibre, then using Sigil in code-view and using several regex's to do the thing's like Header's, broken lines etc..
Now with each of the chapters split properly, the sigil part takes a few minutes, much quicker than what I was doing before. They then just need a quick proofread, to fix any other mistakes.
I'm happy.