The conundrum of Book Five and Book Six is primarily a problem of what the professionals might call "advanced planning." Consequently your writer of pulp has been existentially challenged since about April of this year. "Off the Rails" if you prefer, and it's not a nice feeling. One of the things to keep in mind is in emulating the Great Minds the number Ten is central to your writer of pulp's sense of balance.
There are Ten Commandments, Hegel attempted Ten books, so did Kant, and
generally speaking the Number Ten is a signature of clear thinking. Start
gossiping about Eleven, and it all starts to look like ill-considered chaos. One
solution could be to co-mingle Book Five with Book Six. I could conceptualize it
as Book Five and a Half, think of it as a Beatitude, shove it into the
perfection and simplicity of The Rabbit of Usk, keep Book Five and Half down to
150 pages by using a tiny script. then perhaps I'd get a good night's sleep.