Hi Aaron,
Thanks for taking so much care with this answer. But there's a problem. The viola solo in this (New Complexity) score for a quartet is incredibly dense and fills the whole page to the point that I have to have zero bottom margin. There's very high ledger notes and very low ones, so that staves are large of necessity. I'd do it as a book part, but the problem here is that everything in this score ties across bars and pages, and I don't see how to carry ties across voices between bookparts. This is the basis on which my query was formed.
I conclude that I am snookered. The only option is to break the four staves on the page into two and throw a new page. This upsets the pagination of the work as I have to fit in with hand written fair copy further down the MS as well, for logistical reasons of time at the moment.
I could reduce the top margin for the whole score and position every page except the solo by hand, but this is a lot of work - two hundred pages - and seems to me to be the tail wagging the dog.
Andrew