Sorry for taking a while to respond, I'm not home and accessing my computer via stream is a bit messy, I purchased the book from a site that doesn't have DRM, they just had an M4B as the download to begin with. I can set up a torrent and upload as soon as I'm home, probably on saturday, I hope that's fine!
No hurry.
Take the time to get it right.
If you can, check the metadata of the m4b, see if it has chapters, a cover image, etc.
You can see that using most players or MediaInfo.
Other tools can edit that info.