It occurred to me that I could make judicious use of a little hack element such as:

<pb type="fopFix" /> 

to force pagebreaks where our ancient version of FOP is not able to provide them. Having written the necessary code -- to process the element in the PDF output, and to suppress it in the XHTML -- I found one example in our current data of a heading at the bottom of a page (Conclusions, in the McIntosh paper), and started trying to add the pb, only to discover that I'd deleted it from the schema through my ODD file. Having remedied that, I now find that ROMA isn't able to produce schemas -- it seems to be unresponsive and/or broken, and produces only empty files, where it produces anything at all. I guess I'll come back to this tomorrow.