The Return of Manny Rat

I only found this site a few days ago, and so I've registered for the forum in the hope of some assistance. In reading Margaret Meek's afterword to a particular edition of The Mouse and His Child, I found out that there was a partially written sequel, following which I located and bought the relevant copy of Children's Literature in Education which has a lecture delivered by Russell Hoban in Exeter in 1970 in which he quotes some passages from this sequel. I also know there's some of this in The Russell Hoban Omnibus, and I was wondering if there's more in the latter, or if it's the same stuff.

Any help would be gratefully received, thank you.